Magnetic tape cartridge and magnetic tape device having characterized winding deviation occurrence load

ABSTRACT

The magnetic tape cartridge includes a magnetic tape, and a cartridge reel. In the magnetic tape, a minimum winding deviation occurrence load measured after the magnetic tape is rewound around the cartridge reel by applying a tension of 0.40 N in a longitudinal direction of the magnetic tape is 300 N or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2020-117362 filed on Jul. 7, 2020. The above applicationis hereby expressly incorporated by reference, in its entirety, into thepresent application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape cartridge and amagnetic tape device.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for datastorage such as data back-up or archives (for example, see JP6590102B).

SUMMARY OF THE INVENTION

The recording of data on a magnetic tape is normally performed bycausing the magnetic tape to run in a magnetic tape device (normallyreferred to as a “drive”) and causing a magnetic head to follow a databand of the magnetic tape to record data on the data band. Accordingly,a data track is formed on the data band. In addition, in a case ofreproducing the recorded data, the magnetic tape is caused to run in themagnetic tape device and the magnetic head is caused to follow the databand of the magnetic tape, thereby reading data recorded on the databand. After such recording or reproducing, the magnetic tape is storedwhile being wound around a reel in a magnetic tape cartridge(hereinafter, referred to as a “cartridge reel”), until the nextrecording and/or reproducing is performed.

During the recording and/or the reproducing is performed after thestorage, in a case where the magnetic head for recording and/orreproducing data records and/or reproduces data while being deviatedfrom a target track position due to deformation of the magnetic tape,phenomenons such as overwriting on recorded data, reproducing failure,and the like may occur. Meanwhile, in recent years, in the field of datastorage, there is an increasing need for long-term storage of data,which is called an archive. However, in general, as a storage periodincreases, the magnetic tape tends to be easily deformed. Therefore, itis expected that suppression of the occurrence of the above phenomenonafter storage will be further required in the future.

In view of the above, an object of an aspect of the invention is toprovide a unit for performing recording and/or reproducing in anexcellent manner during recording and/or reproducing of data withrespect to the magnetic tape after storage.

According to an aspect of the invention, there is provided a magnetictape cartridge comprising: a magnetic tape; and a cartridge reel, inwhich, in the magnetic tape, a minimum winding deviation occurrence loadmeasured after the magnetic tape is rewound around the cartridge reel byapplying a tension of 0.40 N (Newton) in a longitudinal direction of themagnetic tape (hereinafter, also referred to as an “minimum windingdeviation occurrence load”) is 300 N or less.

In an embodiment, the magnetic tape may include a non-magnetic supportand a magnetic layer containing a ferromagnetic powder, and thenon-magnetic support may be a polyester support.

In an embodiment, the magnetic tape may further include a non-magneticlayer including a non-magnetic powder between the non-magnetic supportand the magnetic layer.

In an embodiment, the magnetic tape may include a back coating layercontaining a non-magnetic powder on a surface side of the non-magneticsupport opposite to a surface side provided with the magnetic layer.

In an embodiment, the magnetic tape may have a tape thickness of 5.6 μmor less.

In an embodiment, the magnetic tape may have a tape thickness of 5.3 μmor less.

In an embodiment, the minimum winding deviation occurrence load may be10 N to 300 N.

In an embodiment, the magnetic tape cartridge may be used in a magnetictape device. The magnetic tape device may be a magnetic tape device inwhich the magnetic tape is caused to run between a winding reel and thecartridge reel of the magnetic tape cartridge in a state where a tensionis applied in the longitudinal direction of the magnetic tape, a maximumvalue of the tension being 0.50 N or more, and the magnetic tape afterrunning in a state where the tension is applied is caused to be woundaround the cartridge reel by applying a tension of 0.40 N or less in thelongitudinal direction of the magnetic tape.

According to another aspect of the invention, there is provided amagnetic tape device comprising the magnetic tape cartridge.

In an embodiment, the magnetic tape device may include: the magnetictape cartridge; and a winding reel, the magnetic tape is caused to runbetween the winding reel and the cartridge reel of the magnetic tapecartridge in a state where a tension is applied in the longitudinaldirection of the magnetic tape, a maximum value of the tension being0.50 N or more, and the magnetic tape after running in a state where thetension is applied is caused to be wound around the cartridge reel ofthe magnetic tape cartridge by applying a tension of 0.40 N or less inthe longitudinal direction of the magnetic tape.

In an embodiment, the tension applied in the longitudinal direction ofthe magnetic tape during the running may be changed.

According to one aspect of the invention, it is possible to performrecording and/or reproducing in an excellent manner during recordingand/or reproducing of data with respect to the magnetic tape afterstorage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a magnetic tape device.

FIG. 2 shows an example of disposition of data bands and servo bands.

FIG. 3 shows a servo pattern disposition example of a linear-tape-open(LTO) Ultrium format tape.

FIG. 4 is a cross-sectional schematic view showing a testing mechanismfor measuring the minimum winding deviation occurrence load after amagnetic tape is rewound around a cartridge reel by applying a tensionof 0.40 N in a longitudinal direction of the magnetic tape.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to an aspect of the invention, there is provided a magnetictape cartridge including a magnetic tape and a cartridge reel. A minimumwinding deviation occurrence load measured after the magnetic tape isrewound around the cartridge reel by applying a tension of 0.40 N in alongitudinal direction of the magnetic tape is 300 N or less.

In addition, according to another aspect of the invention, there isprovided a magnetic tape device including the magnetic tape cartridge.

The magnetic tape cartridge includes a magnetic tape and a cartridgereel. In an unused magnetic tape cartridge that have not yet beenattached to a magnetic tape device for data recording and/orreproducing, the magnetic tape is typically accommodated while beingwound around a cartridge reel. In the magnetic tape device, the magnetictape can run between the cartridge reel (supply reel) and the windingreel to record data on the magnetic tape and/or reproduce the recordeddata. After the recording or reproducing of data, the magnetic tape isrewound around the cartridge reel, and stored while being wound aroundthe cartridge reel in the magnetic tape cartridge, until the nextrecording and/or reproducing is performed.

It is surmised that different deformations occur depending on theposition such that, during the storage, in the magnetic tapeaccommodated in the magnetic tape cartridge, a part near the cartridgereel is deformed wider than the initial stage due to compressive stressin a tape thickness direction, and a part far from the cartridge reel isdeformed narrower than the initial stage due to the tensile stress inthe tape longitudinal direction. It is considered that, in a case wherethe different deformations occur depending on the position, this maycause the magnetic head to record and/or reproduce data while beingdeviated from the target track position, in a case where the recordingand/or the reproducing is performed after storage.

In regard to the deformation, in the intensive studies of the inventors,the inventors consider that,

(1) the tension applied in the longitudinal direction of the magnetictape in a case of rewinding to the cartridge reel is a low tension of0.40 N or less;

(2) the magnetic tape included in the magnetic tape cartridge is amagnetic tape wound around the cartridge reel without being stronglytightened in a case where it is rewound with such a low tension,

accordingly, it is possible to suppress the occurrence of thedeformation on the magnetic tape during the storage. In this regard, inthe magnetic tape cartridge, a minimum winding deviation occurrence loadmeasured after the magnetic tape is rewound around the cartridge reel byapplying a tension of 0.40 N in the longitudinal direction of themagnetic tape is 300 N or less. The present inventors consider that theminimum winding deviation occurrence load that is 300 N or less,indicates that the magnetic tape can be wound around the cartridge reelwithout being strongly tightened in a case where it is rewound with thelow tension described above. According to such a magnetic tapecartridge, as a result of the intensive studies of the inventors, it wasnewly found that, it is possible to perform recording and/or reproducingin an excellent manner during recording and/or reproducing of data withrespect to the magnetic tape after storage.

Hereinafter, the magnetic tape cartridge and the magnetic tape devicewill be described more specifically. Hereinafter, one embodiment of themagnetic tape cartridge and the magnetic tape device may be describedwith reference to the drawings. However, the magnetic tape cartridge andthe magnetic tape device are not limited to the embodiment shown in thedrawings.

Configuration of Magnetic Tape Device

A magnetic tape device 10 shown in FIG. 1 controls a recording andreproducing head unit 12 in accordance with a command from a controldevice 11 to record and reproduce data on a magnetic tape MT.

The magnetic tape device 10 has a configuration of detecting andadjusting a tension applied in a longitudinal direction of the magnetictape from spindle motors 17A and 17B and driving devices 18A and 18Bwhich rotatably control a cartridge reel 130 and a winding reel 16.

The magnetic tape device 10 has a configuration in which the magnetictape cartridge 13 can be mounted.

The magnetic tape device 10 includes a cartridge memory read and writedevice 14 capable of performing reading and writing with respect to thecartridge memory 131 in the magnetic tape cartridge 13.

An end or a leader pin of the magnetic tape MT is pulled out from themagnetic tape cartridge 13 mounted on the magnetic tape device 10 by anautomatic loading mechanism or manually and passes on a recording andreproducing head through guide rollers 15A and 15B so that a surface ofa magnetic layer of the magnetic tape MT comes into contact with asurface of the recording and reproducing head of the recording andreproducing head unit 12, and accordingly, the magnetic tape MT is woundaround the winding reel 16.

The rotation and torque of the spindle motor 17A and the spindle motor17B are controlled by a signal from the control device 11, and themagnetic tape MT runs at random speed and tension. A servo patternpreviously formed on the magnetic tape can be used to control the tapespeed. A tension detection mechanism may be provided between themagnetic tape cartridge 13 and the winding reel 16 to detect thetension. The tension may be adjusted by using the guide rollers 15A and15B in addition to the control by the spindle motors 17A and 17B.

The cartridge memory read and write device 14 is configured to be ableto read and write information of the cartridge memory 131 according tocommands from the control device 11. As a communication system betweenthe cartridge memory read and write device 14 and the cartridge memory131, for example, an international organization for standardization(ISO) 14443 system can be used.

The control device 11 includes, for example, a controller, a storageunit, a communication unit, and the like.

The recording and reproducing head unit 12 is composed of, for example,a recording and reproducing head, a servo tracking actuator foradjusting a position of the recording and reproducing head in a trackwidth direction, a recording and reproducing amplifier 19, a connectorcable for connecting to the control device 11. The recording andreproducing head is composed of, for example, a recording element forrecording data on a magnetic tape, a reproducing element for reproducingdata of the magnetic tape, and a servo signal reading element forreading a servo signal recorded on the magnetic tape. For example, oneor more of each of the recording elements, the reproducing element, andthe servo signal reading element are mounted in one magnetic head.Alternatively, each element may be separately provided in a plurality ofmagnetic heads according to a running direction of the magnetic tape.

The recording and reproducing head unit 12 is configured to be able torecord data on the magnetic tape MT according to a command from thecontrol device 11. In addition, the data recorded on the magnetic tapeMT can be reproduced according to a command from the control device 11.

The control device 11 has a mechanism of controlling the servo trackingactuator so as to obtain a running position of the magnetic tape from aservo signal read from a servo band during the running of the magnetictape MT and position the recording element and/or the reproducingelement at a target running position (track position). The control ofthe track position is performed by feedback control, for example. Thecontrol device 11 has a mechanism of obtaining a servo band intervalfrom servo signals read from two adjacent servo bands during the runningof the magnetic tape MT. The control device has a mechanism of adjustingand changing the tension applied in the longitudinal direction of themagnetic tape by controlling the torque of the spindle motor 17A and thespindle motor 17B and/or the guide rollers 15A and 15B so that the servoband interval becomes a target value. The adjustment of the tension isperformed by feedback control, for example. In addition, the controldevice 11 can store the obtained information of the servo band intervalin the storage unit inside the control device 11, the cartridge memory131, an external connection device, and the like.

In the magnetic tape device, the tension can be applied in thelongitudinal direction of the magnetic tape during the recording and/orreproducing. The tension applied in the longitudinal direction of themagnetic tape during the recording and/or reproducing is a constantvalue in one embodiment and changes in another embodiment. Regarding thetension in the invention and this specification, in the magnetic tapedevice, the value of the tension applied in the longitudinal directionof the magnetic tape is a value of a tension used for controlling amechanism in which the control device of the magnetic tape deviceadjusts the tension as the tension to be applied in the longitudinaldirection of the magnetic tape. As described above, the tension actuallyapplied in the longitudinal direction of the magnetic tape in themagnetic tape device can be detected by, for example, providing atension detection mechanism between the magnetic tape cartridge 13 andthe winding reel 16 in FIG. 1 . In addition, for example, the tensioncan also be controlled by the control device or the like of the magnetictape device so that a minimum tension is not less than a valuedetermined by a standard or a recommended value and/or a maximum tensionis not greater than a value determined by a standard or a recommendedvalue.

Magnetic Tape Cartridge

In the magnetic tape cartridge before being mounted on the magnetic tapedevice and after being taken out from the magnetic tape device, themagnetic tape is accommodated and wound around the cartridge reel in acartridge main body. The cartridge reel is rotatably comprised in thecartridge main body. As the magnetic tape cartridge, a single reel typemagnetic tape cartridge including one reel in a cartridge main body anda twin reel type magnetic tape cartridge including two reels in acartridge main body are widely used. The magnetic tape cartridgeincluded in the magnetic tape device can be a single reel type magnetictape cartridge in one embodiment, and can be a twin reel type magnetictape cartridge in another embodiment. Regarding the twin reel typemagnetic tape cartridge, the cartridge reel refers to a reel on whichthe magnetic tape is mainly wound, in a case where the magnetic tape isstored after recording and/or reproducing data, and the other reel mayrefer to a winding reel. In a case where the single reel type magnetictape cartridge is mounted in the magnetic tape device in order to recordand/or reproduce data on the magnetic tape, the magnetic tape is drawnfrom the magnetic tape cartridge and wound around the winding reel onthe magnetic tape device, for example, as shown in FIG. 1 . A magnetichead is disposed on a magnetic tape transportation path from themagnetic tape cartridge to a winding reel. The magnetic tape runs byfeeding and winding the magnetic tape between the cartridge reel (alsoreferred to as a “supply reel”) on the magnetic tape cartridge and thewinding reel on the magnetic tape device. In the meantime, the magnetichead comes into contact with and slides on the surface of the magneticlayer of the magnetic tape, and accordingly, the recording and/orreproducing of data is performed. With respect to this, in the twin reeltype magnetic tape cartridge, both reels of the supply reel and thewinding reel are provided in the magnetic tape cartridge.

In one embodiment, the magnetic tape cartridge can include a cartridgememory. The cartridge memory can be, for example, a non-volatile memory,and tension adjustment information is recorded in advance or tensionadjustment information is recorded. The tension adjustment informationis information for adjusting the tension applied in the longitudinaldirection of the magnetic tape. Regarding the cartridge memory, theabove description can also be referred to.

Tension During Running and Tension During Winding on Cartridge Reel

In the magnetic tape device, the magnetic tape can run between thecartridge reel (supply reel) and the winding reel to record data on themagnetic tape and/or reproduce the recorded data. In the magnetic tapedevice described above, the tension can be applied in the longitudinaldirection of the magnetic tape during such running. As a greater tensionis applied in the longitudinal direction of the magnetic tape, adimension of the magnetic tape in a width direction can be more greatlyshrunk (that is, can be further narrowed), and as the tension is small,a degree of the shrinkage can be reduced. Therefore, the dimension ofthe magnetic tape in the width direction can be controlled by the valueof the tension applied in the longitudinal direction of the magnetictape running in the magnetic tape device. In the magnetic tape devicedescribed above, in the one embodiment, the magnetic tape can run in astate where a tension of 0.50 N or more is applied in the longitudinaldirection at the maximum. It is considered that, in a case where themagnetic tape is stored in the magnetic tape cartridge as it is afterrunning with such a great tension, the magnetic tape is likely to bedeformed during the storage. As described above, it is surmised thatdifferent deformations occur depending on the position such that, duringthe storage, in the magnetic tape accommodated in the magnetic tapecartridge, a part near the cartridge reel is deformed wider than theinitial stage due to compressive stress in a tape thickness direction,and a part far from the cartridge reel is deformed narrower than theinitial stage due to the tensile stress in the tape longitudinaldirection. It is considered that, in the magnetic tape accommodated in astate where a great tension is applied, the deformations more greatlyvary depending on position.

Therefore, in the one embodiment, in the magnetic tape device describedabove, in a case where the magnetic tape is wound around the cartridgereel after the running is performed in a state where the tension of 0.50N or more is applied in the longitudinal direction at maximum, thetension applied in the longitudinal direction of the magnetic tape ispreferably 0.40 N or less. Accordingly, the inventors have consideredthat, since the magnetic tape can be wound around the cartridge reelwith a tension smaller than the tension applied in the longitudinaldirection during the running and stored in the magnetic tape cartridge,the occurrence of a phenomenon occurred due to the deformation describedabove can be prevented. In addition, the inventors have surmised that,regardless of whether or not the tension is applied during running andthe tension value, in a case of winding the magnetic tape around thecartridge reel after running, the tension applied in the longitudinaldirection of the magnetic tape set to 0.40 N or less is preferable tosuppress the occurrence of a phenomenon that may occur due to thedeformation described above.

In a case of applying the tension in the longitudinal direction of therunning magnetic tape in the magnetic tape device, a maximum value ofthe tension can be 0.50 N or more, and can also be 0.60 N or more, 0.70N or more, or 0.80 N or more. The maximum value can be, for example,1.50 N or less, 1.40 N or less, 1.30 N or less, 1.20 N or less, 1.10 Nor less, or 1.00 N or less. The tension applied in the longitudinaldirection of the magnetic tape during the running can be a constantvalue or can also be changed. In the case of a constant value, thetension applied in the longitudinal direction of the magnetic tape canbe controlled by, for example, the control device of the magnetic tapedevice so that the tension of a constant value is applied in thelongitudinal direction of the magnetic tape. On the other hand, in acase where the tension applied in the longitudinal direction of themagnetic tape during the running is changed, for example, the dimensioninformation of the magnetic tape in the width direction during therunning can be obtained using a servo signal, and the tension applied inthe longitudinal direction of the magnetic tape can be adjusted andchanged according to the obtained dimension information. Accordingly,the dimension of the magnetic tape in the width direction can becontrolled. One embodiment of such tension adjustment is as describedabove with reference to FIG. 1 . However, the magnetic tape device isnot limited to the exemplified embodiment. In the magnetic tape devicedescribed above, in a case where the tension applied in the longitudinaldirection of the magnetic tape during the running is changed, theminimum value thereof can be, for example, 0.10 N or more, 0.20 N ormore, 0.30 N or more, or 0.40 N or more. In addition, the minimum valuethereof can be, for example, 0.40 N or less or less than 0.40 N in oneembodiment, and can be 0.60 N or less or 0.50 N or less in anotherembodiment.

In the magnetic tape device, in a case where the magnetic tape runs forrecording and/or reproducing data, the following embodiment can beprovided as a specific embodiment of running the magnetic tape.

Embodiment 1: At the end of running for recording and/or reproducingdata, the entire length of the magnetic tape is wound on the windingreel.

Embodiment 2: At the end of running for recording and/or reproducingdata, the entire length of the magnetic tape is wound on the cartridgereel.

Embodiment 3: At the end of running for recording and/or reproducingdata, a part of the magnetic tape is wound around the cartridge reel andanother part thereof is wound around the winding reel.

The tension in a case where the magnetic tape after running is woundaround the cartridge reel by applying tension in the longitudinaldirection of the magnetic tape (hereinafter, also referred to as“rewinding tension”) means the following tension.

In the embodiment 1, the rewinding tension is a tension applied in thelongitudinal direction of the magnetic tape, in a case where the entirelength of the magnetic tape is wound around the cartridge reel to beaccommodated in the magnetic tape cartridge.

In the embodiment 2, first, the magnetic tape is wound from thecartridge reel to the winding reel. In this case, the tension applied inthe longitudinal direction of the magnetic tape is not particularlylimited. The tension may be a constant value, may be changed, may be asin the above description regarding the value of the tension during therunning, or may be not. The tension applied in the longitudinaldirection of the magnetic tape in a case where the magnetic tape issubsequently wound around the cartridge reel is the rewinding tension.The tension is a tension applied in the longitudinal direction of themagnetic tape in a case of winding the entire length of the magnetictape from the winding reel to the cartridge reel.

The embodiment 3 can be any of the following two embodiments. In a firstembodiment (embodiment 3-1), a part of the magnetic tape that is woundaround the cartridge reel, at the end of the running for the recordingand/or the reproducing of data, is wound by applying a tension in thelongitudinal direction during the winding around the cartridge reel. Thetension during the winding is the rewinding tension. A second embodiment(embodiment 3-2) is an embodiment other than the embodiment 3-1 of theembodiment 3. In order to wind the entire length of the magnetic tapearound the cartridge reel and accommodate it in the cartridge, in theembodiment 3-1, the tension applied in the longitudinal direction of themagnetic tape, in a case where the magnetic tape not wound around thecartridge reel is wound around the cartridge reel is the rewindingtension. The embodiment 3-2 is the same as the embodiment 2. That is,first, the magnetic tape is wound from the cartridge reel to the windingreel. The tension applied in the longitudinal direction of the magnetictape in a case of subsequently winding the entire length of the magnetictape from the winding reel to the cartridge reel is the rewindingtension.

In any of the above embodiments 1, 2 and 3, the tension (rewindingtension) applied in the longitudinal direction of the magnetic tape in acase of winding it around the cartridge reel is preferably 0.40 N orless. The rewinding tension may be a constant value or may be changed.In the one embodiment, the rewinding tension may be a constant value of0.40 N or less, or may be changed in s range of 0.40 N or less. In acase of changing, the maximum value of the tension applied in thelongitudinal direction of the magnetic tape in a case of winding itaround the cartridge reel is preferably 0.40 N or less, and can also be,for example, 0.30 N or less. The minimum value of the tension applied inthe longitudinal direction of the magnetic tape in a case of winding itaround the cartridge reel may be, for example, 0.10 N or more or 0.20 Nor more, or may be less than the value exemplified here. The tension(rewinding tension) while winding around the cartridge reel can becontrolled by, for example, the control device of the magnetic tapedevice. In addition, an operation program is recorded in the cartridgememory so that the winding around the cartridge reel is performed byapplying the rewinding tension set after the recording and/orreproducing of data on the magnetic tape in the longitudinal directionof the magnetic tape, and the control device may read this program toexecute the winding operation.

Magnetic Tape

Minimum Winding Deviation Occurrence Load

In the magnetic tape included in the magnetic tape cartridge, a minimumwinding deviation occurrence load measured after the magnetic tape isrewound around the cartridge reel by applying a tension of 0.40 N in thelongitudinal direction of the magnetic tape is 300 N or less. Theminimum winding deviation occurrence load of 300 N or less cancontribute to perform recording and/or reproducing in an excellentmanner during recording and/or reproducing of data with respect to themagnetic tape after storage. From this viewpoint, the minimum windingdeviation occurrence load is more preferably 250 N or less, even morepreferably 200 N or less, and still more preferably 150 N or less. Inaddition, from a viewpoint of improving winding stability of themagnetic tape in a case of being accommodated in the magnetic tapecartridge, the minimum winding deviation occurrence load is preferably 5N or more, more preferably 10 N or more, and even more preferably 15 Nor more.

The minimum winding deviation occurrence load in the present inventionand the present specification is obtained by the following method in anenvironment of an atmosphere temperature of 23° C. and a relativehumidity of 50%.

The magnetic tape cartridge to be measured is an unused magnetic tapecartridge that is not attached to the magnetic tape device.

By winding the magnetic tape wound around the cartridge reel in themagnetic tape cartridge around a temporary winding reel, the entirelength of the magnetic tape is temporarily extracted from the magnetictape cartridge. The extraction is performed by applying a tension of0.40 N in the longitudinal direction of the magnetic tape.

After that, the magnetic tape wound around the temporary winding reel isrewound around the cartridge reel by applying a tension of 0.40 N in thelongitudinal direction of the magnetic tape, and accordingly, the entirelength of the magnetic tape is wound around the cartridge reel again andaccommodated in a magnetic tape cartridge.

The winding and rewinding described above can be performed, for example,by using the magnetic tape device having a mechanism for adjusting thetension described above. The temporary winding reel can be, for example,a winding reel of the magnetic tape device. In the same manner as thetension described above, the tension applied in the longitudinaldirection in the winding and the rewinding is a value of a tension usedfor controlling a mechanism in which the control device of the magnetictape device adjusts the tension as the tension to be applied in thelongitudinal direction of the magnetic tape.

After that, the cartridge reel around which the entire length of themagnetic tape is wound is extracted from the magnetic tape cartridge.The cartridge reel includes at least a reel hub which is a cylindricalmember configuring an axial center portion. In addition, the cartridgereel usually has flanges (upper flange and lower flange) protrudingoutward in a radial direction from an upper end portion and a lower endportion of the reel hub, respectively. For a cartridge reel having aflange, the flange is removed by a well-known cutting unit (ultrasoniccutter or the like) to expose both sides of a tape winding surfacearound which the magnetic tape is wound. The removing of the flange iscarefully performed so that the load in the vertical direction is notapplied to the tape winding surface. A side closer to the reel hub isreferred to as an “inner side”, a farther side is referred to as an“outer side”, an inner end portion of the magnetic tape is referred toas an “inner end portion”, and another end portion is referred to as an“outer end portion”. In a case where a leader pin is joined to the outerend portion, the leader pin is removed and the outer end portion of themagnetic tape is fixed to the tape of the inner side with an adhesivetape, for maintaining the wound state. In a case of pulling the magnetictape during fixing, the magnetic tape is pulled with a low tension (as aguide, the tension in the longitudinal direction is 0.1 N or less) sothat the slack of the magnetic tape can be removed. After that, the reelhub is installed on a cradle, as schematically shown in FIG. 4 . In acase where the gear is integrally molded on the reel hub, the reel hubcan be installed on the cradle so as to be supported by the gearsurface. In a case of installing on the cradle, the reel hub isinstalled on the cradle so that the tape winding surface on a side wherethe plate is placed and the load is applied is separated from a floorsurface on which the cradle is placed by 5 cm or more as a distance in avertical direction as described below. The tape winding surface on theside to which the load is applied may be the tape winding surface oneither side, and is randomly selected. An aluminum ring having an outerdiameter of 90 mm and an inner diameter of 80 mm is placed on the tapewinding surface of the wound magnetic tape installed on the cradle sothat the center of rotation of the reel hub and the center of thealuminum ring match to each other, as schematically illustrated in FIG.4 . The “match” here is not limited to a case of perfect match, and adeviation of 3 mm or less is allowed. On this aluminum ring, an aluminumplate having a square shape of 100 mm×100 mm and a thickness of 3 mm ina plan view is placed. The aluminum plate is schematically illustratedin FIG. 4 . As illustrated by the vertical arrow in FIG. 4 , a load isapplied from the top of the plate and held for 10 minutes, after whichthe load is removed. The load can be applied by a well-known method. Forexample, a load can be applied by placing a weight on the plate or bypressing the plate with a pressing device. The load is preferablyapplied so that a uniform load is applied to the entire surface of theplate. The term “uniform” here also includes the fact that there areportions where the applied load is different within a range that cannormally occur in a case where the load is applied by a well-knownmethod. In addition, in a case of a concentrated load, a region to whichthe load is applied on the plate is a part or all of a circular regionlocated above the range from the center of the ring to 25 mm in theradial direction. In a case where the position in the vertical directionof the upper surface of the plate before applying the load is defined asA, the position in the vertical direction of the upper surface of theplate after removing the load is defined as B, and “A−B≥1 mm” issatisfied, it is determined that the unwinding occurs on the woundmagnetic tape. The measurement of the position in the vertical directionis the position on the ring, in order to avoid the effect of thedeformation of the plate. The positions to be measured are 6 in total atevery 60° in a circumferential direction of the ring, an arithmetic meanof values obtained at the six positions before applying the load isdefined as the A, and an arithmetic mean of values obtained at the sixpositions after removing the load is defined as the B. The position tobe measured for obtaining A and the position to be measured forobtaining B may be the same or different. The load application isstarted from 5 N with respect to the same magnetic tape, the abovemeasurement is performed while increasing the load in increments of 5 N,and the minimum load at which the unwinding occurs is defined as the“minimum winding deviation occurrence load”.

According to the studies of the present inventors regarding the controlof the minimum winding deviation occurrence load of the magnetic tape,the following tendencies are found.

The thinner the tape thickness of the magnetic tape, the smaller thevalue of the minimum winding deviation occurrence load tends to be.

An increase in dispersibility of the ferromagnetic powder in themagnetic layer can contribute to reducing the value of the minimumwinding deviation occurrence load. It is surmised that this is because,as the surface of the magnetic layer is smooth, the tightening tends tohardly occur.

In the magnetic tape including the back coating layer, an increase indispersibility of the non-magnetic powder in the back coating layer cancontribute to reducing the value of the minimum winding deviationoccurrence load. It is surmised that this is because, by increasing thesurface smoothness of the back coating layer, it is possible to suppressthe decrease in surface smoothness of the magnetic layer by transferringthe surface roughness shape of the back coating layer to the surface ofthe magnetic layer.

The details of the above points will be described later.

Hereinafter, the magnetic tape will be described more specifically.

Magnetic Layer

Ferromagnetic Powder

The magnetic tape can include a non-magnetic support, and a magneticlayer including a ferromagnetic powder. As the ferromagnetic powderincluded in the magnetic layer, a well-known ferromagnetic powder can beused as one kind or in combination of two or more kinds as theferromagnetic powder used in the magnetic layer of various magneticrecording media. It is preferable to use a ferromagnetic powder havingan average particle size as the ferromagnetic powder, from a viewpointof improvement of a recording density. From this viewpoint, an averageparticle size of the ferromagnetic powder is preferably equal to orsmaller than 50 nm, more preferably equal to or smaller than 45 nm, evenmore preferably equal to or smaller than 40 nm, further preferably equalto or smaller than 35 nm, further more preferably equal to or smallerthan 30 nm, further even more preferably equal to or smaller than 25 nm,and still preferably equal to or smaller than 20 nm. Meanwhile, from aviewpoint of stability of magnetization, the average particle size ofthe ferromagnetic powder is preferably equal to or greater than 5 nm,more preferably equal to or greater than 8 nm, even more preferablyequal to or greater than 10 nm, still preferably equal to or greaterthan 15 nm, and still more preferably equal to or greater than 20 nm.

Hexagonal Ferrite Powder

As a preferred specific example of the hexagonal ferrite powder and theferromagnetic powder, a hexagonal ferrite powder can be used. Fordetails of the hexagonal ferrite powder, descriptions disclosed inparagraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 ofJP2011-216149A, paragraphs 0013 to 0030 of JP2012-204726A, andparagraphs 0029 to 0084 of JP2015-127985A can be referred to, forexample.

In the invention and the specification, the “hexagonal ferrite powder”is a ferromagnetic powder in which a hexagonal ferrite type crystalstructure is detected as a main phase by X-ray diffraction analysis. Themain phase is a structure to which a diffraction peak at the highestintensity in an X-ray diffraction spectrum obtained by the X-raydiffraction analysis belongs. For example, in a case where thediffraction peak at the highest intensity in the X-ray diffractionspectrum obtained by the X-ray diffraction analysis belongs to ahexagonal ferrite type crystal structure, it is determined that thehexagonal ferrite type crystal structure is detected as a main phase. Ina case where only a single structure is detected by the X-raydiffraction analysis, this detected structure is set as a main phase.The hexagonal ferrite type crystal structure includes at least an ironatom, a divalent metal atom, and an oxygen atom as constituting atoms. Adivalent metal atom is a metal atom which can be divalent cations asions, and examples thereof include an alkali earth metal atom such as astrontium atom, a barium atom, or a calcium atom, and a lead atom. Inthe invention and the specification, the hexagonal strontium ferritepowder is powder in which a main divalent metal atom included in thispowder is a strontium atom, and the hexagonal barium ferrite powder is apowder in which a main divalent metal atom included in this powder is abarium atom. The main divalent metal atom is a divalent metal atomoccupying the greatest content in the divalent metal atom included inthe powder based on atom %. However, the divalent metal atom describedabove does not include rare earth atom. The “rare earth atom” of theinvention and the specification is selected from the group consisting ofa scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. Thelanthanoid atom is selected from the group consisting of a lanthanumatom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymiumatom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europiumatom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosiumatom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom(Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is oneembodiment of the hexagonal ferrite powder will be described morespecifically.

An activation volume of the hexagonal strontium ferrite powder ispreferably 800 to 1,600 nm³. The atomized hexagonal strontium ferritepowder showing the activation volume in the range described above issuitable for manufacturing a magnetic tape exhibiting excellentelectromagnetic conversion characteristics. The activation volume of thehexagonal strontium ferrite powder is preferably equal to or greaterthan 800 nm³, and can also be, for example, equal to or greater than 850nm³. In addition, from a viewpoint of further improving theelectromagnetic conversion characteristics, the activation volume of thehexagonal strontium ferrite powder is more preferably equal to orsmaller than 1,500 nm³, even more preferably equal to or smaller than1,400 nm³, still preferably equal to or smaller than 1,300 nm³, stillmore preferably equal to or smaller than 1,200 nm³, and still even morepreferably equal to or smaller than 1,100 nm³. The same applies to theactivation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and an indexshowing a magnetic magnitude of the particles. Regarding the activationvolume and an anisotropy constant Ku which will be described laterdisclosed in the invention and the specification, magnetic field sweeprates of a coercivity Hc measurement part at time points of 3 minutesand 30 minutes are measured by using an oscillation sample typemagnetic-flux meter (measurement temperature: 23° C.±1° C.), and theactivation volume and the anisotropy constant Ku are values acquiredfrom the following relational expression of Hc and an activation volumeV. A unit of the anisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturationmagnetization (unit: kA/m), k: Boltzmann's constant, T: absolutetemperature (unit: K), V: activation volume (unit: cm³), A: spinprecession frequency (unit: s⁻¹), and t: magnetic field reversal time(unit: s)]

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Thehexagonal strontium ferrite powder can preferably have Ku equal to orgreater than 1.8×10⁵ J/m³, and more preferably have Ku equal to orgreater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontiumferrite powder can be, for example, equal to or smaller than 2.5×10⁵J/m³. However, the high Ku is preferable, because it means high thermalstability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include the rareearth atom. In a case where the hexagonal strontium ferrite powderincludes the rare earth atom, a content (bulk content) of the rare earthatom is preferably 0.5 to 5.0 atom % with respect to 100 atom % of theiron atom. In the one embodiment, the hexagonal strontium ferrite powderincluding the rare earth atom can have a rare earth atom surface layerportion uneven distribution. The “rare earth atom surface layer portionuneven distribution” of the invention and the specification means that acontent of rare earth atom with respect to 100 atom % of iron atom in asolution obtained by partially dissolving the hexagonal strontiumferrite powder with acid (hereinafter, referred to as a “rare earth atomsurface layer portion content” or simply a “surface layer portioncontent” regarding the rare earth atom) and a content of rare earth atomwith respect to 100 atom % of iron atom in a solution obtained bytotally dissolving the hexagonal strontium ferrite powder with acid(hereinafter, referred to as a “rare earth atom bulk content” or simplya “bulk content” regarding the rare earth atom) satisfy a ratio of rareearth atom surface layer portion content/rare earth atom bulk content>1.0.

The content of rare earth atom of the hexagonal strontium ferrite powderwhich will be described later is identical to the rare earth atom bulkcontent. With respect to this, the partial dissolving using acid is todissolve the surface layer portion of particles configuring thehexagonal strontium ferrite powder, and accordingly, the content of rareearth atom in the solution obtained by the partial dissolving is thecontent of rare earth atom in the surface layer portion of the particlesconfiguring the hexagonal strontium ferrite powder. The rare earth atomsurface layer portion content satisfying a ratio of “rare earth atomsurface layer portion content/rare earth atom bulk content >1.0” meansthat the rare earth atoms are unevenly distributed in the surface layerportion (that is, a larger amount of the rare earth atoms is present,compared to that inside), among the particles configuring the hexagonalstrontium ferrite powder. The surface layer portion of the invention andthe specification means a part of the region of the particlesconfiguring the hexagonal strontium ferrite powder towards the insidefrom the surface.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, a content (bulk content) of the rare earth atom ispreferably 0.5 to 5.0 atom % with respect to 100 atom % of the ironatom. It is thought that the rare earth atom having the bulk content inthe range described above and uneven distribution of the rare earth atomin the surface layer portion of the particles configuring the hexagonalstrontium ferrite powder contribute to the prevention of a decrease inreproducing output during the repeated reproducing. It is surmised thatthis is because the rare earth atom having the bulk content in the rangedescribed above included in the hexagonal strontium ferrite powder andthe uneven distribution of the rare earth atom in the surface layerportion of the particles configuring the hexagonal strontium ferritepowder can increase the anisotropy constant Ku. As the value of theanisotropy constant Ku is high, occurrence of a phenomenon calledthermal fluctuation (that is, improvement of thermal stability) can beprevented. By preventing the occurrence of the thermal fluctuation, adecrease in reproducing output during the repeated reproducing can beprevented. It is surmised that the uneven distribution of the rare earthatom in the surface layer portion of the particles of the hexagonalstrontium ferrite powder contributes to stabilization of a spin at aniron (Fe) site in a crystal lattice of the surface layer portion,thereby increasing the anisotropy constant Ku.

In addition, it is surmised that the use of the hexagonal strontiumferrite powder having the rare earth atom surface layer portion unevendistribution as the ferromagnetic powder of the magnetic layer alsocontributes to the prevention of chipping of the surface of the magneticlayer due to the sliding with the magnetic head. That is, it is surmisedthat, the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution can also contribute to theimprovement of running durability of the magnetic tape. It is surmisedthat this is because the uneven distribution of the rare earth atom onthe surface of the particles configuring the hexagonal strontium ferritepowder contributes to improvement of an interaction between the surfaceof the particles and an organic substance (for example, binding agentand/or additive) included in the magnetic layer, thereby improvinghardness of the magnetic layer.

From a viewpoint of preventing reduction of the reproduction output inthe repeated reproduction and/or a viewpoint of further improvingrunning durability, the content of rare earth atom (bulk content) ismore preferably in a range of 0.5 to 4.5 atom %, even more preferably ina range of 1.0 to 4.5 atom %, and still preferably in a range of 1.5 to4.5 atom %.

The bulk content is a content obtained by totally dissolving thehexagonal strontium ferrite powder. In the invention and thespecification, the content of the atom is a bulk content obtained bytotally dissolving the hexagonal strontium ferrite powder, unlessotherwise noted. The hexagonal strontium ferrite powder including therare earth atom may include only one kind of rare earth atom or mayinclude two or more kinds of rare earth atom, as the rare earth atom. Ina case where two or more kinds of rare earth atom are included, the bulkcontent is obtained from the total of the two or more kinds of rareearth atom. The same also applies to the other components of theinvention and the specification. That is, for a given component, onlyone kind may be used or two or more kinds may be used, unless otherwisenoted. In a case where two or more kinds are used, the content is acontent of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, the rare earth atom included therein may be any one or morekinds of the rare earth atom. Examples of the rare earth atom preferablefrom a viewpoint of preventing reduction of the reproduction outputduring the repeated reproduction include a neodymium atom, a samariumatom, an yttrium atom, and a dysprosium atom, a neodymium atom, asamarium atom, an yttrium atom are more preferable, and a neodymium atomis even more preferable.

In the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution, a degree of unevendistribution of the rare earth atom is not limited, as long as the rareearth atom is unevenly distributed in the surface layer portion of theparticles configuring the hexagonal strontium ferrite powder. Forexample, regarding the hexagonal strontium ferrite powder having therare earth atom surface layer portion uneven distribution, a ratio ofthe surface layer portion content of the rare earth atom obtained bypartial dissolving performed under the dissolving conditions which willbe described later and the bulk content of the rare earth atom obtainedby total dissolving performed under the dissolving conditions which willbe described later, “surface layer portion content/bulk content” isgreater than 1.0 and can be equal to or greater than 1.5. The “surfacelayer portion content/bulk content” greater than 1.0 means that the rareearth atoms are unevenly distributed in the surface layer portion (thatis, a larger amount of the rare earth atoms is present, compared to thatinside), in the particles configuring the hexagonal strontium ferritepowder. A ratio of the surface layer portion content of the rare earthatom obtained by partial dissolving performed under the dissolvingconditions which will be described later and the bulk content of therare earth atom obtained by total dissolving performed under thedissolving conditions which will be described later, “surface layerportion content/bulk content” can be, for example, equal to or smallerthan 10.0, equal to or smaller than 9.0, equal to or smaller than 8.0,equal to or smaller than 7.0, equal to or smaller than 6.0, equal to orsmaller than 5.0, or equal to or smaller than 4.0. However, in thehexagonal strontium ferrite powder having the rare earth atom surfacelayer portion uneven distribution, the “surface layer portioncontent/bulk content” is not limited to the exemplified upper limit orthe lower limit, as long as the rare earth atom is unevenly distributedin the surface layer portion of the particles configuring the hexagonalstrontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonalstrontium ferrite powder will be described below. Regarding thehexagonal strontium ferrite powder present as the powder, sample powderfor the partial dissolving and the total dissolving are collected frompowder of the same batch. Meanwhile, regarding the hexagonal strontiumferrite powder included in a magnetic layer of a magnetic tape, a partof the hexagonal strontium ferrite powder extracted from the magneticlayer is subjected to the partial dissolving and the other part issubjected to the total dissolving. The extraction of the hexagonalstrontium ferrite powder from the magnetic layer can be performed by amethod disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonalstrontium ferrite powder remaining in the solution can be visuallyconfirmed in a case of the completion of the dissolving. For example, byperforming the partial dissolving, a region of the particles configuringthe hexagonal strontium ferrite powder which is 10% to 20% by mass withrespect to 100% by mass of a total of the particles can be dissolved. Onthe other hand, the total dissolving means dissolving performed untilthe hexagonal strontium ferrite powder remaining in the solution is notvisually confirmed in a case of the completion of the dissolving.

The partial dissolving and the measurement of the surface layer portioncontent are, for example, performed by the following method. However,dissolving conditions such as the amount of sample powder and the likedescribed below are merely examples, and dissolving conditions capableof performing the partial dissolving and the total dissolving can berandomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 1 mol/L is held on ahot plate at a set temperature of 70° C. for 1 hour. The obtainedsolution is filtered with a membrane filter having a hole diameter of0.1 μm. The element analysis of the filtrate obtained as described aboveis performed by an inductively coupled plasma (ICP) analysis device. Bydoing so, the surface layer portion content of the rare earth atom withrespect to 100 atom % of the iron atom can be obtained. In a case wherea plurality of kinds of rare earth atoms are detected from the elementanalysis, a total content of the entirety of the rare earth atoms is thesurface layer portion content. The same applies to the measurement ofthe bulk content.

Meanwhile, the total dissolving and the measurement of the bulk contentare, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 4 mol/L is held on ahot plate at a set temperature of 80° C. for 3 hours. After that, theprocess is performed in the same manner as in the partial dissolving andthe measurement of the surface layer portion content, and the bulkcontent with respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regards to this point, in hexagonal strontium ferritepowder which includes the rare earth atom but does not have the rareearth atom surface layer portion uneven distribution, σs tends tosignificantly decrease, compared to that in hexagonal strontium ferritepowder not including the rare earth atom. With respect to this, it isthought that, hexagonal strontium ferrite powder having the rare earthatom surface layer portion uneven distribution is also preferable forpreventing such a significant decrease in σs. In one embodiment, σs ofthe hexagonal strontium ferrite powder can be equal to or greater than45 A·m²/kg and can also be equal to or greater than 47 A·m²/kg. On theother hand, from a viewpoint of noise reduction, σs is preferably equalto or smaller than 80 A·m²/kg and more preferably equal to or smallerthan 60 A·m²/kg. σs can be measured by using a well-known measurementdevice capable of measuring magnetic properties such as an oscillationsample type magnetic-flux meter. In the invention and the specification,the mass magnetization σs is a value measured at a magnetic fieldstrength of 15 kOe, unless otherwise noted. 1 [kOe]=(10⁶/4π) [A/m].

Regarding the content (bulk content) of the constituting atom in thehexagonal strontium ferrite powder, a content of the strontium atom canbe, for example, 2.0 to 15.0 atom % with respect to 100 atom % of theiron atom. In one embodiment, in the hexagonal strontium ferrite powder,the divalent metal atom included in this powder can be only a strontiumatom. In another embodiment, the hexagonal strontium ferrite powder canalso include one or more kinds of other divalent metal atoms, inaddition to the strontium atom. For example, the hexagonal strontiumferrite powder can include a barium atom and/or a calcium atom. In acase where the other divalent metal atom other than the strontium atomis included, a content of a barium atom and a content of a calcium atomin the hexagonal strontium ferrite powder respectively can be, forexample, 0.05 to 5.0 atom % with respect to 100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbitetype (also referred to as an “M type”), a W type, a Y type, and a Z typeare known. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be confirmed by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more kinds of crystal structure can be detected bythe X-ray diffraction analysis. For example, in one embodiment, in thehexagonal strontium ferrite powder, only the M type crystal structurecan be detected by the X-ray diffraction analysis. For example, the Mtype hexagonal ferrite is represented by a compositional formula ofAFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where thehexagonal strontium ferrite powder has the M type, A is only a strontiumatom (Sr), or in a case where a plurality of divalent metal atoms areincluded as A, the strontium atom (Sr) occupies the hexagonal strontiumferrite powder with the greatest content based on atom % as describedabove. A content of the divalent metal atom in the hexagonal strontiumferrite powder is generally determined according to the type of thecrystal structure of the hexagonal ferrite and is not particularlylimited. The same applies to a content of an iron atom and a content ofan oxygen atom. The hexagonal strontium ferrite powder at least includesan iron atom, a strontium atom, and an oxygen atom, and can also includea rare earth atom. In addition, the hexagonal strontium ferrite powdermay or may not include atoms other than these atoms. As an example, thehexagonal strontium ferrite powder may include an aluminum atom (Al). Acontent of the aluminum atom can be, for example, 0.5 to 10.0 atom %with respect to 100 atom % of the iron atom. From a viewpoint ofpreventing the reduction of the reproduction output during the repeatedreproduction, the hexagonal strontium ferrite powder includes the ironatom, the strontium atom, the oxygen atom, and the rare earth atom, anda content of the atoms other than these atoms is preferably equal to orsmaller than 10.0 atom %, more preferably 0 to 5.0 atom %, and may be 0atom % with respect to 100 atom % of the iron atom. That is, in oneembodiment, the hexagonal strontium ferrite powder may not include atomsother than the iron atom, the strontium atom, the oxygen atom, and therare earth atom. The content shown with atom % described above isobtained by converting a value of the content (unit: % by mass) of eachatom obtained by totally dissolving the hexagonal strontium ferritepowder into a value shown as atom % by using the atomic weight of eachatom. In addition, in the invention and the specification, a given atomwhich is “not included” means that the content thereof obtained byperforming total dissolving and measurement by using an ICP analysisdevice is 0% by mass. A detection limit of the ICP analysis device isgenerally equal to or smaller than 0.01 ppm (parts per million) based onmass. The expression “not included” is used as a meaning including thata given atom is included with the amount smaller than the detectionlimit of the ICP analysis device. In one embodiment, the hexagonalstrontium ferrite powder does not include a bismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, aferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, an ε-ironoxide powder can also be used. In the invention and the specification,the “ε-iron oxide powder” is a ferromagnetic powder in which an ε-ironoxide type crystal structure is detected as a main phase by X-raydiffraction analysis. For example, in a case where the diffraction peakat the highest intensity in the X-ray diffraction spectrum obtained bythe X-ray diffraction analysis belongs to an ε-iron oxide type crystalstructure, it is determined that the ε-iron oxide type crystal structureis detected as a main phase. As a manufacturing method of the ε-ironoxide powder, a manufacturing method from a goethite, a reverse micellemethod, and the like are known. All of the manufacturing methods arewell known. For the method of manufacturing the ε-iron oxide powder inwhich a part of Fe is substituted with substitutional atoms such as Ga,Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. PowderMetallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mater. Chem. C,2013, 1, pp. 5200-5206 can be referred, for example. However, themanufacturing method of the ε-iron oxide powder capable of being used asthe ferromagnetic powder in the magnetic layer of the magnetic tape isnot limited to the method described here.

An activation volume of the ε-iron oxide powder is preferably 300 to1,500 nm³. The atomized ε-iron oxide powder showing the activationvolume in the range described above is suitable for manufacturing amagnetic tape exhibiting excellent electromagnetic conversioncharacteristics. The activation volume of the ε-iron oxide powder ispreferably equal to or greater than 300 nm³, and can also be, forexample, equal to or greater than 500 nm³. In addition, from a viewpointof further improving the electromagnetic conversion characteristics, theactivation volume of the ε-iron oxide powder is more preferably equal toor smaller than 1,400 nm³, even more preferably equal to or smaller than1,300 nm³, still preferably equal to or smaller than 1,200 nm³, andstill more preferably equal to or smaller than 1,100 nm³.

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Theε-iron oxide powder can preferably have Ku equal to or greater than3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, forexample, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku ispreferable, because it means high thermal stability, and thus, Ku is notlimited to the exemplified value.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regard to this point, in one embodiment, σs of theε-iron oxide powder can be equal to or greater than 8 A·m²/kg and canalso be equal to or greater than 12 A·m²/kg. On the other hand, from aviewpoint of noise reduction, σs of the ε-iron oxide powder ispreferably equal to or smaller than 40 A·m²/kg and more preferably equalto or smaller than 35 A·m²/kg.

In the invention and the specification, average particle sizes ofvarious powder such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at an imaging magnification ratio of 100,000 with atransmission electron microscope, the image is printed on photographicprinting paper or displayed on a display so that the total magnificationratio of 500,000 to obtain an image of particles configuring the powder.A target particle is selected from the obtained image of particles, anoutline of the particle is traced with a digitizer, and a size of theparticle (primary particle) is measured. The primary particle is anindependent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesarbitrarily extracted. An arithmetic mean of the particle size of 500particles obtained as described above is the average particle size ofthe powder. As the transmission electron microscope, a transmissionelectron microscope H-9000 manufactured by Hitachi, Ltd. can be used,for example. In addition, the measurement of the particle size can beperformed by a well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the invention and thespecification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an embodiment in which particles configuringthe aggregate are directly in contact with each other, but also includesan embodiment in which a binding agent or an additive which will bedescribed later is interposed between the particles. A term, particlesmay be used for representing the powder.

As a method for collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted,

(1) in a case where the shape of the particle observed in the particleimage described above is a needle shape, a fusiform shape, or a columnarshape (here, a height is greater than a maximum long diameter of abottom surface), the size (particle size) of the particles configuringthe powder is shown as a length of a long axis configuring the particle,that is, a long axis length,

(2) in a case where the shape of the particle is a planar shape or acolumnar shape (here, a thickness or a height is smaller than a maximumlong diameter of a plate surface or a bottom surface), the particle sizeis shown as a maximum long diameter of the plate surface or the bottomsurface, and

(3) in a case where the shape of the particle is a sphere shape, apolyhedron shape, or an unspecified shape, and the long axis configuringthe particles cannot be specified from the shape, the particle size isshown as an equivalent circle diameter. The equivalent circle diameteris a value obtained by a circle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a short axis, that is, a short axis length of the particles ismeasured in the measurement described above, a value of (long axislength/short axis length) of each particle is obtained, and anarithmetic mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the shortaxis length as the definition of the particle size is a length of ashort axis configuring the particle, in a case of (2), the short axislength is a thickness or a height, and in a case of (3), the long axisand the short axis are not distinguished, thus, the value of (long axislength/short axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average long axislength, and in a case of the definition (2), the average particle sizeis an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50% to 90% by mass and more preferably 60%to 90% by mass. A high filling percentage of the ferromagnetic powder inthe magnetic layer is preferable from a viewpoint of improvement ofrecording density.

Binding Agent

The magnetic tape may be a coating type magnetic tape, and can include abinding agent in the magnetic layer. The binding agent is one or morekinds of resin. As the binding agent, various resins normally used as abinding agent of a coating type magnetic recording medium can be used.As the binding agent, a resin selected from a polyurethane resin, apolyester resin, a polyamide resin, a vinyl chloride resin, an acrylicresin obtained by copolymerizing styrene, acrylonitrile, or methylmethacrylate, a cellulose resin such as nitrocellulose, an epoxy resin,a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetalor polyvinyl butyral can be used alone or a plurality of resins can bemixed with each other to be used. Among these, a polyurethane resin, anacrylic resin, a cellulose resin, and a vinyl chloride resin arepreferable. These resins may be a homopolymer or a copolymer. Theseresins can be used as the binding agent even in the non-magnetic layerand/or a back coating layer which will be described later.

For the binding agent described above, descriptions disclosed inparagraphs 0028 to 0031 of JP2010-024113A can be referred to. An averagemolecular weight of the resin used as the binding agent can be, forexample, 10,000 to 200,000 as a weight-average molecular weight. Theamount of the binding agent used can be, for example, 1.0 to 30.0 partsby mass with respect to 100.0 parts by mass of the ferromagnetic powder.

Curing Agent

A curing agent can also be used together with the resin which can beused as the binding agent. As the curing agent, in one embodiment, athermosetting compound which is a compound in which a curing reaction(crosslinking reaction) proceeds due to heating can be used, and inanother embodiment, a photocurable compound in which a curing reaction(crosslinking reaction) proceeds due to light irradiation can be used.At least a part of the curing agent is included in the magnetic layer ina state of being reacted (crosslinked) with other components such as thebinding agent, by proceeding the curing reaction in the magnetic layerforming step. This point is the same as regarding a layer formed byusing a composition, in a case where the composition used for formingthe other layer includes the curing agent. The preferred curing agent isa thermosetting compound, and polyisocyanate is suitable. For thedetails of polyisocyanate, descriptions disclosed in paragraphs 0124 and0125 of JP2011-216149A can be referred to. The amount of the curingagent can be, for example, 0 to 80.0 parts by mass with respect to 100.0parts by mass of the binding agent in the magnetic layer formingcomposition, and is preferably 50.0 to 80.0 parts by mass, from aviewpoint of improvement of hardness of the magnetic layer.

Additives

The magnetic layer may include one or more kinds of additives, asnecessary. As the additives, the curing agent described above is used asan example. In addition, examples of the additive included in themagnetic layer include a non-magnetic powder (for example, inorganicpowder, carbon black, or the like), a lubricant, a dispersing agent, adispersing assistant, a fungicide, an antistatic agent, and anantioxidant. For the lubricant, a description disclosed in paragraphs0030 to 0033, 0035, and 0036 of JP2016-126817A can be referred to. Thelubricant may be included in the non-magnetic layer which will bedescribed later. For the lubricant which can be included in thenon-magnetic layer, a description disclosed in paragraphs 0030, 0031,0034 to 0036 of JP2016-126817A can be referred to. For the dispersingagent, a description disclosed in paragraphs 0061 and 0071 ofJP2012-133837A can be referred to. In addition, a compound having apolyalkyleneimine chain and a vinyl polymer chain can exhibit a functionas a dispersing agent for improving the dispersibility of theferromagnetic powder. Further, the compound described above can alsocontribute to improving the hardness of the magnetic layer. An increasein hardness of the magnetic layer can contribute to the increase insurface smoothness of the magnetic layer by suppressing the occurrenceof offset, which will be described later. For the compound having apolyalkyleneimine chain and a vinyl polymer chain, paragraphs 0024 to0064 of JP2019-169225A and examples of JP2019-169225A can be referredto. The magnetic layer preferably contains 0.5 parts by mass or more,more preferably 1.0 parts by mass or more, even more preferably 3.0parts by mass or more, still preferably 5.0 parts by mass or more, stillmore preferably 10.0 parts by mass or more, still even more preferably15.0 parts by mass or more of the compound with respect to 100.0 partsby mass of the ferromagnetic powder. In addition, the content of thecompound in the magnetic layer is preferably 25.0 parts by mass or lesswith respect to 100.0 parts by mass of the ferromagnetic powder. One ormore dispersing agent such as the compound described above and the likemay be added to a non-magnetic layer forming composition. For thedispersing agent which can be added to the non-magnetic layer formingcomposition, a description disclosed in paragraph 0061 of JP2012-133837Acan be referred to. As the non-magnetic powder which may be included inthe magnetic layer, non-magnetic powder which can function as anabrasive, non-magnetic powder (for example, non-magnetic colloidparticles) which can function as a projection formation agent whichforms projections suitably protruded from the surface of the magneticlayer, and the like can be used. An average particle size of colloidalsilica (silica colloid particles) shown in the examples which will bedescribed later is a value obtained by a method disclosed in ameasurement method of an average particle diameter in a paragraph 0015of JP2011-048878A. As the additives, a commercially available productcan be suitably selected according to the desired properties ormanufactured by a well-known method, and can be used with any amount. Asan example of the additive which can be used for improvingdispersibility of the abrasive in the magnetic layer including theabrasive, a dispersing agent disclosed in paragraphs 0012 to 0022 ofJP2013-131285A can be used.

The magnetic layer described above can be provided on the surface of thenon-magnetic support directly or indirectly through the non-magneticlayer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on the surface of the non-magneticsupport or may include a magnetic layer on the surface of thenon-magnetic support through the non-magnetic layer including thenon-magnetic powder. The non-magnetic powder used in the non-magneticlayer may be a powder of an inorganic substance or a powder of anorganic substance. In addition, carbon black and the like can be used.Examples of powder of the inorganic substance include powder of metal,metal oxide, metal carbonate, metal sulfate, metal nitride, metalcarbide, and metal sulfide. The non-magnetic powder can be purchased asa commercially available product or can be manufactured by a well-knownmethod. For details thereof, descriptions disclosed in paragraphs 0146to 0150 of JP2011-216149A can be referred to. For carbon black which canbe used in the non-magnetic layer, descriptions disclosed in paragraphs0040 and 0041 of JP2010-024113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably 50% to 90% by mass and more preferably 60% to 90% by mass.

The non-magnetic layer can include a binding agent and can also includeadditives. In regards to other details of a binding agent or additivesof the non-magnetic layer, the well-known technology regarding thenon-magnetic layer can be applied. In addition, in regards to the typeand the content of the binding agent, and the type and the content ofthe additive, for example, the well-known technology regarding themagnetic layer can be applied.

The non-magnetic layer of the invention and the specification alsoincludes a substantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Back Coating Layer

In the one embodiment, the magnetic tape may further include a backcoating layer containing a non-magnetic powder on a surface side of thenon-magnetic support opposite to the surface side provided with themagnetic layer. In addition, in another embodiment, the magnetic tapecan also be a magnetic tape having no back coating layer. In a casewhere the magnetic tape includes a back coating layer, the followingdescription can be referred to for the non-magnetic powder of the backcoating layer. The back coating layer can include a binding agent andcan also include one or more additives. In regards to the binding agentincluded in the back coating layer and additives, a well-knowntechnology regarding the back coating layer can be applied, and awell-known technology regarding the list of the magnetic layer and/orthe non-magnetic layer can also be applied. For example, for the backcoating layer, descriptions disclosed in paragraphs 0018 to 0020 ofJP2006-331625A and page 4, line 65, to page 5, line 38, of U.S. Pat. No.7,029,774B can be referred to.

In a manufacturing step and the like of the magnetic tape, the surfaceshape of the rear surface is transferred to the surface of the magneticlayer (so-called offset) while the front surface and the rear surface ofthe magnetic layer are in contact with each other in a rolled state,thereby forming a recess on the surface of the magnetic layer. Anincrease in surface smoothness of the magnetic layer by suppressing theformation of the recess can contribute to reducing the value of theminimum winding deviation occurrence load. The rear surface is thesurface of the back coating layer in a case of including the backcoating layer, is a surface of the support in a case of not includingthe back coating layer. As an example of a unit for suppressing theformation of recess on the surface of the magnetic layer, a type ofcomponent to be added to the composition for forming the back coatinglayer, for example, can be selected, in order to adjust the surfaceshape of the rear surface. From this viewpoint, as the non-magneticpowder of the back coating layer, it is preferable that carbon black anda non-magnetic powder other than carbon black are used in combination,or carbon black is used (that is, the non-magnetic powder of the backcoating layer consists of carbon black). Examples of the non-magneticpowder other than carbon black include the non-magnetic powderexemplified above as one that can be contained in the non-magneticlayer. Regarding the non-magnetic powder of the back coating layer, apercentage of carbon black with respect to 100.0 parts by mass of thetotal amount of the non-magnetic powder is preferably in a range of 50.0to 100.0 parts by mass, more preferably in a range of 70.0 to 100.0parts by mass, even more preferably in a range of 90.0 to 100.0 parts bymass. In addition, it is also preferable that the total amount of thenon-magnetic powder in the back coating layer is carbon black. Thecontent of the non-magnetic powder in the back coating layer ispreferably in a range of 50 to 90% by mass and more preferably in arange of 60 to 90% by mass, with respect to the total mass of the backcoating layer.

In order to suppress the occurrence of the offset, the back coatinglayer forming composition preferably contains a component (dispersingagent) capable of increasing the dispersibility of the non-magneticpowder contained in this composition. As an example of such a dispersingagent, a compound having an ammonium salt structure of an alkyl esteranion represented by Formula 1 can be used. A compound having anammonium salt structure of an alkyl ester anion represented by Formula 1can contribute to improving the dispersibility of carbon black. The“alkyl ester anion” can also be referred to as an “alkyl carboxylateanion”.

In Formula 1, R represents an alkyl group having 7 or more carbon atomsor a fluorinated alkyl group having 7 or more carbon atoms, and Z⁺represents an ammonium cation.

In addition, in one embodiment, two or more kinds of components capableof forming the compound having a salt structure can be used in a case ofpreparing the back coating layer forming composition. Accordingly, in acase of preparing the back coating layer forming composition, at leastsome of these components can form the compound having the saltstructure.

Unless otherwise noted, groups described below may have a substituent ormay be unsubstituted. In addition, the “number of carbon atoms” of agroup having a substituent means the number of carbon atoms notincluding the number of carbon atoms of the substituent, unlessotherwise noted. In the present invention and the specification,examples of the substituent include an alkyl group (for example, analkyl group having 1 to 6 carbon atoms), a hydroxy group, an alkoxygroup (for example, an alkoxy group having 1 to 6 carbon atoms), ahalogen atom (for example, a fluorine atom, a chlorine atom, a bromineatom, or the like), a cyano group, an amino group, a nitro group, anacyl group, a carboxy group, salt of a carboxy group, a sulfonic acidgroup, and salt of a sulfonic acid group.

Hereinafter, Formula 1 will be described in more detail.

In Formula 1, R represents an alkyl group having 7 or more carbon atomsor a fluorinated alkyl group having 7 or more carbon atoms. Thefluorinated alkyl group has a structure in which some or all of thehydrogen atoms constituting the alkyl group are substituted with afluorine atom. The alkyl group or fluorinated alkyl group represented byR may have a linear structure, a branched structure, may be a cyclicalkyl group or fluorinated alkyl group, and preferably has a linearstructure. The alkyl group or fluorinated alkyl group represented by Rmay have a substituent, may be unsubstituted, and is preferablyunsubstituted. The alkyl group represented by R can be represented by,for example, C_(n)H_(2n+1)—. Here, n represents an integer of 7 or more.In addition, the fluorinated alkyl group represented by R may have astructure in which a part or all of the hydrogen atoms constituting thealkyl group represented by C_(n)H_(2n+1)— are substituted with afluorine atom. The alkyl group or fluorinated alkyl group represented byR has 7 or more carbon atoms, preferably 8 or more carbon atoms, morepreferably 9 or more carbon atoms, further preferably 10 or more carbonatoms, still preferably 11 or more carbon atoms, still more preferably12 or more carbon atoms, and still even more preferably 13 or morecarbon atoms. The alkyl group or fluorinated alkyl group represented byR has preferably 20 or less carbon atoms, more preferably 19 or lesscarbon atoms, and even more preferably 18 or less carbon atoms.

In Formula 1, Z⁺ represents an ammonium cation. Specifically, theammonium cation has the following structure. In the present inventionand the present specification, “*” in the formulas that represent a partof the compound represents a bonding position between the structure ofthe part and the adjacent atom.

The nitrogen cation N⁺ of the ammonium cation and the oxygen anion O⁻ inFormula 1 may form a salt bridging group to form the ammonium saltstructure of the alkyl ester anion represented by Formula 1. The factthat the compound having the ammonium salt structure of the alkyl esteranion represented by Formula 1 is contained in the back coating layercan be confirmed by performing analysis with respect to the magnetictape by X-ray photoelectron spectroscopy (electron spectroscopy forchemical analysis (ESCA)), infrared spectroscopy (IR), or the like.

In the one embodiment, the ammonium cation represented by Z⁺ can beprovided by, for example, the nitrogen atom of the nitrogen-containingpolymer becoming a cation. The nitrogen-containing polymer means apolymer containing a nitrogen atom. In the present invention and thepresent specification, a term “polymer” means to include both ahomopolymer and a copolymer. The nitrogen atom can be included as anatom configuring a main chain of the polymer in one embodiment, and canbe included as an atom constituting a side chain of the polymer in oneembodiment.

As one embodiment of the nitrogen-containing polymer, polyalkyleneiminecan be used. The polyalkyleneimine is a ring-opening polymer ofalkyleneimine and is a polymer having a plurality of repeating unitsrepresented by Formula 2.

The nitrogen atom N configuring the main chain in Formula 2 can beconverted to a nitrogen cation N⁺ to provide an ammonium cationrepresented by Z⁺ in Formula 1. Then, an ammonium salt structure can beformed with the alkyl ester anion, for example, as follows.

Hereinafter, Formula 2 will be described in more detail.

In Formula 2, R¹ and R² each independently represent a hydrogen atom oran alkyl group, and n1 represents an integer of 2 or more.

Examples of the alkyl group represented by R¹ or R² include an alkylgroup having 1 to 6 carbon atoms, preferably an alkyl group having 1 to3 carbon atoms, more preferably a methyl group or an ethyl group, andeven more preferably a methyl group. The alkyl group represented by R¹or R² is preferably an unsubstituted alkyl group. A combination of R¹and R² in Formula 2 is a form in which one is a hydrogen atom and theother is an alkyl group, a form in which both are hydrogen atoms, and aform in which both are an alkyl group (the same or different alkylgroups), and is preferably a form in which both are hydrogen atoms. Asthe alkyleneimine that provides the polyalkyleneimine, a structure ofthe ring that has the smallest number of carbon atoms is ethyleneimine,and the main chain of the alkyleneimine (ethyleneimine) obtained by ringopening of ethyleneimine has 2 carbon atoms. Accordingly, n1 in Formula2 is 2 or more. n1 in Formula 2 can be, for example, 10 or less, 8 orless, 6 or less, or 4 or less. The polyalkyleneimine may be ahomopolymer containing only the same structure as the repeatingstructure represented by Formula 2, or may be a copolymer containing twoor more different structures as the repeating structure represented byFormula 2. A number average molecular weight of the polyalkyleneiminethat can be used to form the compound having the ammonium salt structureof the alkyl ester anion represented by Formula 1 can be, for example,equal to or greater than 200, and is preferably equal to or greater than300, and more preferably equal to or greater than 400. In addition, thenumber average molecular weight of the polyalkyleneimine can be, forexample, equal to or less than 10,000, and is preferably equal to orless than 5,000 and more preferably equal to or less than 2,000.

In the present invention and the present specification, the averagemolecular weight (weight-average molecular weight and number averagemolecular weight) is measured by gel permeation chromatography (GPC) andis a value obtained by performing standard polystyrene conversion.Unless otherwise noted, the average molecular weights shown in theexamples which will be described below are values(polystyrene-equivalent values) obtained by standard polystyreneconversion of the values measured under the following measurementconditions using GPC.

GPC device: HLC-8220 (manufactured by Tosoh Corporation)

Guard Column: TSK guard column Super HZM-H

Column: TSK gel Super HZ 2000, TSK gel Super HZ 4000, TSK gel Super HZ-M(manufactured by Tosoh Corporation, 4.6 mm (inner diameter)×15.0 cm,three kinds of columns are linked in series)

Eluent: Tetrahydrofuran (THF), including stabilizer(2,6-di-t-butyl-4-methylphenol)

Eluent flow rate: 0.35 mL/min

Column temperature: 40° C.

Inlet temperature: 40° C.

Refractive index (RI) measurement temperature: 40° C.

Sample concentration: 0.3% by mass

Sample injection amount: 10 μL

In addition, as the other embodiment of the nitrogen-containing polymer,polyallylamine can be used. The polyallylamine is a polymer ofallylamine and is a polymer having a plurality of repeating unitsrepresented by Formula 3.

The nitrogen atom N configuring an amino group of a side chain inFormula 3 can be converted to a nitrogen cation N⁺ to provide anammonium cation represented by Z⁺ in Formula 1. Then, an ammonium saltstructure can be formed with the alkyl ester anion, for example, asfollows.

A weight-average molecular weight of the polyallylamine that can be usedto form the compound having the ammonium salt structure of the alkylester anion represented by Formula 1 can be, for example, equal to orgreater than 200, and is preferably equal to or greater than 1,000, andmore preferably equal to or greater than 1,500. In addition, theweight-average molecular weight of the polyalkyleneimine can be, forexample, equal to or less than 15,000, and is preferably equal to orless than 10,000 and more preferably equal to or less than 8,000.

The fact that the compound having a structure derived frompolyalkyleneimine or polyallylimine as the compound having the ammoniumsalt structure of the alkyl ester anion represented by Formula 1 isincluded in the back coating layer can be confirmed by analyzing thesurface of the back coating layer by a time-of-flight secondary ion massspectrometry (TOF-SIMS) or the like.

The compound having the ammonium salt structure of the alkyl ester anionrepresented by Formula 1 can be salt of a nitrogen-containing polymerand one or more fatty acids selected from the group consisting of fattyacids having 7 or more carbon atoms and fluorinated fatty acids having 7or more carbon atoms. The nitrogen-containing polymer forming salt canbe one kind or two or more kinds of nitrogen-containing polymers, andcan be, for example, a nitrogen-containing polymer selected from thegroup consisting of polyalkyleneimine and polyallylamine. The fattyacids forming the salt can be one kind or two or more kinds of fattyacids selected from the group consisting of fatty acids having 7 or morecarbon atoms and fluorinated fatty acids having 7 or more carbon atoms.The fluorinated fatty acid has a structure in which some or all of thehydrogen atoms configuring the alkyl group bonded to a carboxy groupCOOH in the fatty acid are substituted with fluorine atoms. For example,the salt forming reaction can easily proceed by mixing thenitrogen-containing polymer and the fatty acids described above at roomtemperature. The room temperature is, for example, approximately 20° C.to 25° C. In the one embodiment, one or more kinds ofnitrogen-containing polymers and one or more kinds of the fatty acidsdescribed above are used as components of the back coating layer formingcomposition, and the salt forming reaction can proceed by mixing thesein the step of preparing the back coating layer forming composition. Inthe one embodiment, one or more kinds of nitrogen-containing polymersand one or more kinds of the fatty acids described above are mixed toform a salt before preparing the back coating layer forming composition,and then, the back coating layer forming composition can be preparedusing this salt as a component of the back coating layer formingcomposition. In a case where the nitrogen-containing polymer and thefatty acid are mixed to form an ammonium salt of the alkyl ester anionrepresented by Formula 1, the nitrogen atom configuring thenitrogen-containing polymer and the carboxy group of the fatty acid maybe reacted to form the following structure, and a form including such astructure are also included in the above compound.

Examples of the fatty acids include fatty acids having an alkyl groupdescribed above as R in Formula 1 and fluorinated fatty acids having afluorinated alkyl group described above as R in Formula 1.

A mixing ratio of the nitrogen-containing polymer and the fatty acidused to form the compound having the ammonium salt structure of thealkyl ester anion represented by Formula 1 is preferably 10:90 to 90:10,more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20,as a mass ratio of nitrogen-containing polymer:fatty acid. In addition,the used amount of the compound having the ammonium salt structure ofthe alkyl ester anion represented by Formula 1 can be 1.0 to 20.0 partsby mass and is preferably 1.0 to 10.0 parts by mass with respect to100.0 parts by mass of carbon black, during preparation of the backcoating layer forming composition. In addition, for example, in a caseof preparing the back coating layer forming composition, 0.1 to 10.0parts by mass of the nitrogen-containing polymer can be used and 0.5 to8.0 parts by mass of the nitrogen-containing polymer is preferably usedwith respect to 100.0 parts by mass of carbon black. The used amount ofthe fatty acids described above can be, for example, 0.05 to 10.0 partsby mass and is preferably 0.1 to 5.0 parts by mass, with respect to100.0 parts by mass of carbon black.

Non-Magnetic Support

As the non-magnetic support (hereinafter, also simply referred to as a“support”), well-known components such as polyethylene terephthalate,polyethylene naphthalate, polyamide, polyamide imide, aromatic polyamideare used. Among these, polyethylene terephthalate and polyethylenenaphthalate, are preferable.

In the one embodiment, the non-magnetic support of the magnetic tape canbe a polyester support. In the present invention and the presentspecification, “polyester” means a resin containing a plurality of esterbonds. The “polyester support” means a support that includes at leastone layer of polyester film. The “polyester film” is a film in which thelargest component in the component configuring this film based on massis polyester. The “polyester support” of the invention and thespecification includes a support in which all of resin films included inthis support is the polyester film and a support including the polyesterfilm and the other resin film. Specific examples of the polyestersupport include a single polyester film, a laminated film of two or morelayers of the polyester film having the same constituting component, alaminated film of two or more layers of the polyester film havingdifferent constituting components, and a laminated film including one ormore layers of the polyester film and one or more layers of resin filmother than the polyester. In the laminated film, an adhesive layer orthe like may be randomly included between two adjacent layers. Inaddition, the polyester support may randomly include a metal film and/ora metal oxide film formed by performing vapor deposition or the like onone or both surfaces. The same applies to an “aromatic polyestersupport”, a “polyethylene terephthalate support” and a “polyethylenenaphthalate support” in the invention and the specification.

The polyester support can be an aromatic polyester support. In theinvention and the specification, “aromatic polyester” means a resinincluding an aromatic skeleton and a plurality of ester bonds, and the“aromatic polyester support” means a support including at least onelayer of an aromatic polyester film.

An aromatic ring included in an aromatic skeleton including the aromaticpolyester is not particularly limited. Specific examples of the aromaticring include a benzene ring and naphthalene ring.

For example, polyethylene terephthalate (PET) is polyester including abenzene ring, and is a resin obtained by polycondensation of ethyleneglycol and terephthalic acid and/or dimethyl terephthalate. The“polyethylene terephthalate” of the invention and the specificationincludes polyethylene terephthalate having a structure including one ormore kinds of other components (for example, copolymerization component,and component introduced to a terminal or a side chain), in addition tothe component described above.

Polyethylene naphthalate (PEN) is polyester including a naphthalenering, and is a resin obtained by performing esterification reaction ofdimethyl 2,6-naphthalenedicarboxylate and ethylene glycol, and then,transesterification and polycondensation reaction. The “polyethylenenaphthalate” of the invention and the specification includespolyethylene naphthalate having a structure including one or more kindsof other components (for example, copolymerization component, andcomponent introduced to a terminal or a side chain), in addition to thecomponent described above.

In addition, the non-magnetic support can be a biaxial stretching film,and may be a film subjected to corona discharge, plasma treatment, easyadhesion treatment, or heat treatment.

Various Thicknesses

Regarding a thickness (total thickness) of the magnetic tape, it hasbeen required to increase recording capacity (increase in capacity) ofthe magnetic tape along with the enormous increase in amount ofinformation in recent years. As a unit for increasing the capacity, athickness of the magnetic tape is reduced and a length of the magnetictape accommodated in one reel of the magnetic tape cartridge isincreased. From this point, the thickness (total thickness) of themagnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm orless, even more preferably 5.4 μm or less, still preferably 5.3 μm orless, still more preferably 5.2 μm or less, still even more preferably5.1 μm or less. As described above, reducing the thickness of themagnetic tape can contribute to reducing the value of the minimumwinding deviation occurrence load. In addition, from a viewpoint of easeof handling, the thickness of the magnetic tape is preferably 3.0 μm ormore and more preferably 3.5 μm or more.

The thickness (total thickness) of the magnetic tape can be measured bythe following method.

Ten tape samples (for example, length of 5 to 10 cm) are cut out from arandom portion of the magnetic tape, these tape samples are overlapped,and the thickness is measured. A value which is one tenth of themeasured thickness (thickness per one tape sample) is set as the tapethickness. The thickness measurement can be performed using a well-knownmeasurement device capable of performing the thickness measurement at0.1 μm order.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to asaturation magnetization amount of a magnetic head used, a head gaplength, a recording signal band, and the like, is normally 0.01 μm to0.15 μm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03μm to 0.1 μm, from a viewpoint of realization of high-density recording.The magnetic layer may be at least single layer, the magnetic layer maybe separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is the totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably 0.9 μm or less andmore preferably 0.1 to 0.7 μm.

Various thicknesses such as the thickness of the magnetic layer and thelike can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction isexposed with an ion beam and the cross section observation of theexposed cross section is performed using a scanning electron microscopeor a transmission electron microscope. Various thicknesses can beobtained as the arithmetic mean of the thicknesses obtained at tworandom portions in the cross section observation. Alternatively, variousthicknesses can be obtained as a designed thickness calculated under themanufacturing conditions.

Manufacturing Step

Preparation of Each Layer Forming Composition

A Step of preparing a composition for forming the magnetic layer, thenon-magnetic layer or the back coating layer can generally include atleast a kneading step, a dispersing step, and a mixing step providedbefore and after these steps, in a case where necessary. Each step maybe divided into two or more stages. The component used in thepreparation of each layer forming composition may be added at an initialstage or in a middle stage of each step. As the solvent, one kind or twoor more kinds of various kinds of solvents usually used for producing acoating type magnetic recording medium can be used. For the solvent, adescription disclosed in a paragraph 0153 of JP2011-216149A can bereferred to, for example. In addition, each component may be separatelyadded in two or more steps. For example, a binding agent may beseparately added in a kneading step, a dispersing step, and a mixingstep for adjusting viscosity after the dispersion. In order tomanufacture the magnetic tape, a well-known manufacturing technology canbe used in various steps. In the kneading step, an open kneader, acontinuous kneader, a pressure kneader, or a kneader having a strongkneading force such as an extruder is preferably used. For details ofthe kneading processes, descriptions disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-079274A (JP-H01-079274A) can be referred to.As a disperser, a well-known dispersion device can be used. Thefiltering may be performed by a well-known method in any stage forpreparing each layer forming composition. The filtering can be performedby using a filter, for example. As the filter used in the filtering, afilter having a hole diameter of 0.01 to 3 μm (for example, filter madeof glass fiber or filter made of polypropylene) can be used, forexample.

Coating Step

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the surface of the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. The back coating layer can be formed by applying the back coatinglayer forming composition onto the surface of the non-magnetic supportopposite to the surface provided with the non-magnetic layer and/or themagnetic layer (or non-magnetic layer and/or the magnetic layer is to beprovided). For details of the coating for forming each layer, adescription disclosed in a paragraph 0066 of JP2010-231843A can bereferred to.

Other Steps

For various other steps for manufacturing the magnetic tape, awell-known technology can be applied. For details of the various steps,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to, for example. For example, the coating layer of themagnetic layer forming composition can be subjected to an alignmentprocess in an alignment zone, while the coating layer is wet. For thealignment process, various technologies disclosed in a paragraph 0052 ofJP2010-024113A can be applied. For example, a homeotropic alignmentprocess can be performed by a well-known method such as a method using adifferent polar facing magnet. In the alignment zone, a drying speed ofthe coating layer can be controlled by a temperature and an air flow ofthe dry air and/or a transporting rate in the alignment zone. Inaddition, the coating layer may be preliminarily dried beforetransporting to the alignment zone.

Through various steps, a long magnetic tape raw material can beobtained. The obtained magnetic tape raw material is cut (slit) by awell-known cutter to have a width of a magnetic tape to be wound aroundthe magnetic tape cartridge. The width is determined according to thestandard and is normally ½ inches. ½ inches=12.65 mm.

In the magnetic tape obtained by slitting, a servo pattern can beformed. The servo pattern will be described later in detail.

Heat Treatment

In the one embodiment, the magnetic tape can be a magnetic tapemanufactured through the following heat treatment. In anotherembodiment, the magnetic tape can be manufactured without the followingheat treatment.

As the heat treatment, the magnetic tape slit and cut to have a widthdetermined according to the standard described above can be wound arounda core member and can be subjected to the heat treatment in the woundstate.

In the one embodiment, the heat treatment is performed in a state wherethe magnetic tape is wound around the core member for heat treatment(hereinafter, referred to as a “core for heat treatment”), the magnetictape after the heat treatment is wound around a cartridge reel of themagnetic tape cartridge, and a magnetic tape cartridge in which themagnetic tape is wound around the cartridge reel can be manufactured.

The core for heat treatment can be formed of metal, a resin, or paper.The material of the core for heat treatment is preferably a materialhaving high stiffness, from a viewpoint of preventing the occurrence ofa winding defect such as spoking or the like. From this viewpoint, thecore for heat treatment is preferably formed of metal or a resin. Inaddition, as an index for stiffness, a modulus of bending elasticity ofthe material for the core for heat treatment is preferably equal to orgreater than 0.2 GPa (gigapascals) and more preferably equal to orgreater than 0.3 GPa. Meanwhile, since the material having highstiffness is normally expensive, the use of the core for heat treatmentof the material having stiffness exceeding the stiffness capable ofpreventing the occurrence of the winding defect causes the costincrease. By considering the viewpoint described above, the modulus ofbending elasticity of the material for the core for heat treatment ispreferably equal to or smaller than 250 GPa. The modulus of bendingelasticity is a value measured based on international organization forstandardization (ISO) 178 and the modulus of bending elasticity ofvarious materials is well known. In addition, the core for heattreatment can be a solid or hollow core member. In a case of a hollowshape, a wall thickness is preferably equal to or greater than 2 mm,from a viewpoint of maintaining the stiffness. In addition, the core forheat treatment may include or may not include a flange.

The magnetic tape having a length equal to or greater than a length tobe finally accommodated in the magnetic tape cartridge (hereinafter,referred to as a “final product length”) is prepared as the magnetictape wound around the core for heat treatment, and it is preferable toperform the heat treatment by placing the magnetic tape in the heattreatment environment, in a state where the magnetic tape is woundaround the core for heat treatment. The magnetic tape length woundaround the core for heat treatment is equal to or greater than the finalproduct length, and is preferably the “final product length+α”, from aviewpoint of ease of winding around the core for heat treatment. This ais preferably equal to or greater than 5 m, from a viewpoint of ease ofthe winding. The tension in a case of winding around the core for heattreatment is preferably equal to or greater than 0.1 N. In addition,from a viewpoint of preventing the occurrence of excessive deformationduring the manufacturing, the tension in a case of winding around thecore for heat treatment is preferably equal to or smaller than 1.5 N andmore preferably equal to or smaller than 1.0 N. An outer diameter of thecore for heat treatment is preferably equal to or greater than 20 mm andmore preferably equal to or greater than 40 mm, from viewpoints of easeof the winding and preventing coiling (curl in longitudinal direction).The outer diameter of the core for heat treatment is preferably equal toor smaller than 100 mm and more preferably equal to or smaller than 90mm. A width of the core for heat treatment may be equal to or greaterthan the width of the magnetic tape wound around this core. In addition,after the heat treatment, in a case of detaching the magnetic tape fromthe core for heat treatment, it is preferable that the magnetic tape andthe core for heat treatment are sufficiently cooled and magnetic tape isdetached from the core for heat treatment, in order to prevent theoccurrence of the tape deformation which is not intended during thedetaching operation. It is preferable the detached magnetic tape iswound around another core temporarily (referred to as a “core fortemporary winding”), and the magnetic tape is wound around a cartridgereel (generally, outer diameter is approximately 40 to 50 mm) of themagnetic tape cartridge from the core for temporary winding.Accordingly, a relationship between the inside and the outside withrespect to the core for heat treatment of the magnetic tape in a case ofthe heat treatment can be maintained and the magnetic tape can be woundaround the cartridge reel of the magnetic tape cartridge. Regarding thedetails of the core for temporary winding and the tension in a case ofwinding the magnetic tape around the core, the description describedabove regarding the core for heat treatment can be referred to. In anembodiment in which the heat treatment is subjected to the magnetic tapehaving a length of the “final product length+α”, the lengthcorresponding to “+α” may be cut in any stage. For example, in oneembodiment, the magnetic tape having the final product length may bewound around the cartridge reel of the magnetic tape cartridge from thecore for temporary winding and the remaining length corresponding the“+α” may be cut. From a viewpoint of decreasing the amount of theportion to be cut out and removed, the a is preferably equal to orsmaller than 20 m.

The specific embodiment of the heat treatment performed in a state ofbeing wound around the core member as described above is describedbelow.

An atmosphere temperature for performing the heat treatment(hereinafter, referred to as a “heat treatment temperature”) ispreferably equal to or higher than 40° C. and more preferably equal toor higher than 50° C. On the other hand, from a viewpoint of preventingthe excessive deformation, the heat treatment temperature is preferablyequal to or lower than 75° C., more preferably equal to or lower than70° C., and even more preferably equal to or lower than 65° C.

A weight absolute humidity of the atmosphere for performing the heattreatment is preferably equal to or greater than 0.1 g/kg Dry air andmore preferably equal to or greater than 1 g/kg Dry air. The atmospherein which the weight absolute humidity is in the range described above ispreferable, because it can be prepared without using a special devicefor decreasing moisture. On the other hand, the weight absolute humidityis preferably equal to or smaller than 70 g/kg Dry air and morepreferably equal to or smaller than 66 g/kg Dry air, from a viewpoint ofpreventing a deterioration in workability by dew condensation. The heattreatment time is preferably equal to or longer than 0.3 hours and morepreferably equal to or longer than 0.5 hours. In addition, the heattreatment time is preferably equal to or shorter than 48 hours, from aviewpoint of production efficiency.

Servo Pattern

The “formation of the servo pattern” can be “recording of a servosignal”. The dimension information of the magnetic tape in the widthdirection during the running can be obtained using a servo signal, andthe dimension of the magnetic tape in the width direction can becontrolled by adjusting and changing the tension applied in thelongitudinal direction of the magnetic tape according to the obtaineddimension information.

The formation of the servo pattern will be described below.

The servo pattern is generally formed along a longitudinal direction ofthe magnetic tape. As a system of control using a servo signal (servocontrol), timing-based servo (TBS), amplitude servo, or frequency servois used.

As shown in European Computer Manufacturers Association (ECMA)-319 (June2001), a timing-based servo system is used in a magnetic tape based on alinear-tape-open (LTO) standard (generally referred to as an “LTOtape”). In this timing-based servo system, the servo pattern isconfigured by continuously disposing a plurality of pairs of magneticstripes (also referred to as “servo stripes”) not parallel to each otherin a longitudinal direction of the magnetic tape. The servo system is asystem of performing head tracking using a servo signal. In theinvention and the specification, the “timing-based servo pattern” refersto a servo pattern that enables head tracking in a servo system of atiming-based servo system. As described above, a reason for that theservo pattern is configured with one pair of magnetic stripes notparallel to each other is because a servo signal reading element passingon the servo pattern recognizes a passage position thereof.Specifically, one pair of the magnetic stripes are formed so that a gapthereof is continuously changed along the width direction of themagnetic tape, and a relative position of the servo pattern and theservo signal reading element can be recognized, by the reading of thegap thereof by the servo signal reading element. The information of thisrelative position can realize the tracking of a data track. Accordingly,a plurality of servo tracks are generally set on the servo pattern alongthe width direction of the magnetic tape.

The servo band is configured of a servo patterns continuous in thelongitudinal direction of the magnetic tape. A plurality of servo bandsare normally provided on the magnetic tape. For example, the numberthereof is 5 in the LTO tape. A region interposed between two adjacentservo bands is a data band. The data band is configured of a pluralityof data tracks and each data track corresponds to each servo track.

In one embodiment, as shown in JP2004-318983A, information showing thenumber of servo band (also referred to as “servo band identification(ID)” or “Unique Data Band Identification Method (UDIM) information”) isembedded in each servo band. This servo band ID is recorded by shiftinga specific servo stripe among the plurality of pair of servo stripes inthe servo band so that the position thereof is relatively deviated inthe longitudinal direction of the magnetic tape. Specifically, theposition of the shifted specific servo stripe among the plurality ofpair of servo stripes is changed for each servo band. Accordingly, therecorded servo band ID becomes unique for each servo band, andtherefore, the servo band can be uniquely specified by only reading oneservo band by the servo signal reading element.

In a method of uniquely specifying the servo band, a staggered method asshown in ECMA-319 (June 2001) is used. In this staggered method, aplurality of the groups of one pair of magnetic stripes (servo stripe)not parallel to each other which are continuously disposed in thelongitudinal direction of the magnetic tape is recorded so as to beshifted in the longitudinal direction of the magnetic tape for eachservo band. A combination of this shifted servo band between theadjacent servo bands is set to be unique in the entire magnetic tape,and accordingly, the servo band can also be uniquely specified byreading of the servo pattern by two servo signal reading elements.

In addition, as shown in ECMA-319 (June 2001), information showing theposition in the longitudinal direction of the magnetic tape (alsoreferred to as “Longitudinal Position (LPOS) information”) is normallyembedded in each servo band. This LPOS information is recorded so thatthe position of one pair of servo stripes are shifted in thelongitudinal direction of the magnetic tape, in the same manner as theUDIM information. However, unlike the UDIM information, the same signalis recorded on each servo band in this LPOS information.

Other information different from the UDIM information and the LPOSinformation can be embedded in the servo band. In this case, theembedded information may be different for each servo band as the UDIMinformation, or may be common in all of the servo bands, as the LPOSinformation.

In addition, as a method of embedding the information in the servo band,a method other than the method described above can be used. For example,a predetermined code may be recorded by thinning out a predeterminedpair among the group of pairs of the servo stripes.

A servo pattern forming head is also referred to as a servo write head.The servo write head generally includes pairs of gaps corresponding tothe pairs of magnetic stripes by the number of servo bands. In general,a core and a coil are respectively connected to each of the pairs ofgaps, and a magnetic field generated in the core can generate leakagemagnetic field in the pairs of gaps, by supplying a current pulse to thecoil. In a case of forming the servo pattern, by inputting a currentpulse while causing the magnetic tape to run on the servo write head,the magnetic pattern corresponding to the pair of gaps is transferred tothe magnetic tape, and the servo pattern can be formed. A width of eachgap can be suitably set in accordance with a density of the servopattern to be formed. The width of each gap can be set as, for example,equal to or smaller than 1 μm, 1 to 10 μm, or equal to or greater than10 μm.

Before forming the servo pattern on the magnetic tape, a demagnetization(erasing) process is generally performed on the magnetic tape. Thiserasing process can be performed by applying a uniform magnetic field tothe magnetic tape by using a DC magnet and an AC magnet. The erasingprocess includes direct current (DC) erasing and alternating current(AC) erasing. The AC erasing is performed by slowing decreasing anintensity of the magnetic field, while reversing a direction of themagnetic field applied to the magnetic tape. Meanwhile, the DC erasingis performed by applying the magnetic field in one direction to themagnetic tape. The DC erasing further includes two methods. A firstmethod is horizontal DC erasing of applying the magnetic field in onedirection along a longitudinal direction of the magnetic tape. A secondmethod is vertical DC erasing of applying the magnetic field in onedirection along a thickness direction of the magnetic tape. The erasingprocess may be performed with respect to all of the magnetic tape or maybe performed for each servo band of the magnetic tape.

A direction of the magnetic field to the servo pattern to be formed isdetermined in accordance with the direction of erasing. For example, ina case where the horizontal DC erasing is performed to the magnetictape, the formation of the servo pattern is performed so that thedirection of the magnetic field and the direction of erasing is oppositeto each other. Accordingly, the output of the servo signal obtained bythe reading of the servo pattern can be increased. As disclosed inJP2012-053940A, in a case where the magnetic pattern is transferred tothe magnetic tape subjected to the vertical DC erasing by using the gap,the servo signal obtained by the reading of the formed servo pattern hasa unipolar pulse shape. Meanwhile, in a case where the magnetic patternis transferred to the magnetic tape subjected to the horizontal DCerasing by using the gap, the servo signal obtained by the reading ofthe formed servo pattern has a bipolar pulse shape.

Magnetic Head

In the invention and the specification, the “magnetic tape device” meansa device capable of performing at least one of the recording of data onthe magnetic tape or the reproducing of data recorded on the magnetictape. Such a device is generally called a drive. The magnetic headincluded in the magnetic tape device can be a recording head capable ofperforming the recording of data on the magnetic tape, and can also be areproducing head capable of performing the reproducing of data recordedon the magnetic tape. In addition, in the embodiment, the magnetic tapedevice can include both of a recording head and a reproducing head asseparate magnetic heads. In another embodiment, the magnetic headincluded in the magnetic tape device may have a configuration in whichboth the recording element and the reproducing element are comprised inone magnetic head. As the reproducing head, a magnetic head (MR head)including a magnetoresistive (MR) element capable of reading informationrecorded on the magnetic tape with excellent sensitivity as thereproducing element is preferable. As the MR head, various well-known MRheads (for example, a Giant Magnetoresistive (GMR) head, or a TunnelMagnetoresistive (TMR) head) can be used. In addition, the magnetic headwhich performs the recording of data and/or the reproducing of data mayinclude a servo pattern reading element. Alternatively, as a head otherthan the magnetic head which performs the recording of data and/or thereproducing of data, a magnetic head (servo head) including a servopattern reading element may be included in the magnetic tape device. Forexample, the magnetic head which performs the recording of data and/orreproducing of the recorded data (hereinafter, also referred to as a“recording and reproducing head”) can include two servo signal readingelements, and each of the two servo signal reading elements can read twoadjacent servo bands with the data band interposed therebetween at thesame time. One or a plurality of elements for data can be disposedbetween the two servo signal reading elements. The element for recordingdata (recording element) and the element for reproducing data(reproducing element) are collectively referred to as “elements fordata”.

By reproducing data using the reproducing element having a narrowreproducing element width as the reproducing element, the data recordedat high density can be reproduced with high sensitivity. From thisviewpoint, the reproducing element width of the reproducing element ispreferably 0.8 μm or less. The reproducing element width of thereproducing element can be, for example, 0.3 μm or more. However, it isalso preferable to fall below this value from the above viewpoint.

On the other hand, as the reproducing element width decreases, aphenomenon such as reproducing failure due to off-track is more likelyto occur. In order to suppress the occurrence of such a phenomenon, itis preferable to use a magnetic tape device that controls the dimensionof the magnetic tape in the width direction by adjusting and changingthe tension applied in the longitudinal direction of the magnetic tapeduring the running.

Here, the “reproducing element width” refers to a physical dimension ofthe reproducing element width. Such physical dimensions can be measuredwith an optical microscope, a scanning electron microscope, or the like.

In a case of recording data and/or reproducing recorded data, first,head tracking can be performed using a servo signal. That is, as theservo signal reading element follows a predetermined servo track, theelement for data can be controlled to pass on the target data track. Themovement of the data track is performed by changing the servo track tobe read by the servo signal reading element in the tape width direction.

In addition, the recording and reproducing head can perform therecording and/or reproducing with respect to other data bands. In thiscase, the servo signal reading element is moved to a predetermined servoband by using the UDIM information described above, and the trackingwith respect to the servo band may be started.

FIG. 2 shows an example of disposition of data bands and servo bands. InFIG. 2 , a plurality of servo bands 1 are disposed to be interposedbetween guide bands 3 in a magnetic layer of a magnetic tape MT. Aplurality of regions 2 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in an LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 3 are formed on a servo band, in a case ofmanufacturing a magnetic tape. Specifically, in FIG. 3 , a servo frameSF on the servo band 1 is configured with a servo sub-frame 1 (SSF1) anda servo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with anA burst (in FIG. 3 , reference numeral A) and a B burst (in FIG. 3 ,reference numeral B). The A burst is configured with servo patterns A1to A5 and the B burst is configured with servo patterns B1 to B5.Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG. 3, reference numeral C) and a D burst (in FIG. 3, reference numeral D).The C burst is configured with servo patterns C1 to C4 and the D burstis configured with servo patterns D1 to D4. Such 18 servo patterns aredisposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the setsof 5 servo patterns and 4 servo patterns, and are used for recognizingthe servo frames. FIG. 3 shows one servo frame for explaining. However,in practice, in the magnetic layer of the magnetic tape in which thehead tracking servo in the timing-based servo system is performed, aplurality of servo frames are disposed in each servo band in a runningdirection. In FIG. 3 , an arrow shows the running direction. Forexample, an LTO Ultrium format tape generally includes 5,000 or moreservo frames per a tape length of 1 m, in each servo band of themagnetic layer.

EXAMPLES

Hereinafter, one embodiment of the invention will be described withreference to examples. However, the invention is not limited toembodiments shown in the examples. “Parts” and “%” in the followingdescription mean “parts by mass” and “% by mass”, unless otherwisenoted. “eq” indicates equivalent and a unit not convertible into SIunit.

In addition, various steps and operations described below were performedin an environment of a temperature of 20° C. to 25° C. and a relativehumidity of 40% to 60%, unless otherwise noted.

Non-Magnetic Support

In Table 1 which will be described later, “PEN” indicates a polyethylenenaphthalate support and “PET” indicates a polyethylene terephthalatesupport.

Ferromagnetic Powder

In Table 1, “BaFe” in a column of the type of the ferromagnetic powderis a hexagonal barium ferrite powder having an average particle size(average plate diameter) of 21 nm.

In Table 1, “SrFe1” of the column of the type of ferromagnetic powderindicates a hexagonal strontium ferrite powder produced as follows.

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixed ina mixer to obtain a raw material mixture.

The obtained raw material mixture was melted in a platinum crucible at amelting temperature of 1,390° C., and a tap hole provided on the bottomof the platinum crucible was heated while stirring the melt, and themelt was tapped in a rod shape at approximately 6 g/sec. The tap liquidwas rolled and cooled with a water cooling twin roller to prepare anamorphous body.

280 g of the prepared amorphous body was put into an electronic furnace,heated to 635° C. (crystallization temperature) at a rate of temperaturerise of 3.5° C./min, and held at the same temperature for 5 hours, andhexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1,000 g of zirconia beads having a particle diameter of 1 mm,and 800 ml of an acetic acid aqueous solution having a concentration of1% were added to a glass bottle, and a dispersion process was performedin a paint shaker for 3 hours. After that, the obtained dispersionliquid and the beads were separated and put in a stainless still beaker.The dispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 18 nm, an activation volume was 902nm³, an anisotropy constant Ku was 2.2×10⁵ J/m³, and a massmagnetization σs was 49 A·m²/kg.

12 mg of a sample powder was collected from the hexagonal strontiumferrite powder obtained as described above, the element analysis of afiltrate obtained by the partial dissolving of this sample powder underthe dissolving conditions described above was performed by the ICPanalysis device, and a surface layer portion content of a neodymium atomwas obtained.

Separately, 12 mg of a sample powder was collected from the hexagonalstrontium ferrite powder obtained as described above, the elementanalysis of a filtrate obtained by the total dissolving of this samplepowder under the dissolving conditions described above was performed bythe ICP analysis device, and a bulk content of a neodymium atom wasobtained.

The content (bulk content) of the neodymium atom in the hexagonalstrontium ferrite powder obtained as described above with respect to 100atom % of iron atom was 2.9 atom %. In addition, the surface layerportion content of the neodymium atom was 8.0 atom %. A ratio of thesurface layer portion content and the bulk content, “surface layerportion content/bulk content” was 2.8 and it was confirmed that theneodymium atom is unevenly distributed on the surface layer of theparticles.

A crystal structure of the hexagonal ferrite shown by the powderobtained as described above was confirmed by scanning CuKα ray under theconditions of a voltage of 45 kV and intensity of 40 mA and measuring anX-ray diffraction pattern under the following conditions (X-raydiffraction analysis). The powder obtained as described above showed acrystal structure of magnetoplumbite type (M type) hexagonal ferrite. Inaddition, a crystal phase detected by the X-ray diffraction analysis wasa magnetoplumbite type single phase.

PANalytical X'Pert Pro diffractometer, PIXcel detector

Soller slit of incident beam and diffraction beam: 0.017 radians

Fixed angle of dispersion slit: ¼ degrees

Mask: 10 mm

Scattering prevention slit: ¼ degrees

Measurement mode: continuous

Measurement time per 1 stage: 3 seconds

Measurement speed: 0.017 degrees per second

Measurement step: 0.05 degree

In Table 1, “SrFe2” of the column of the type of ferromagnetic powderindicates a hexagonal strontium ferrite powder produced as follows.

1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g of Al(OH)₃, 34g of CaCO₃, and 141 g of BaCO₃ were weighed and mixed in a mixer toobtain a raw material mixture.

The obtained raw material mixture was melted in a platinum crucible at amelting temperature of 1,380° C., and a tap hole provided on the bottomof the platinum crucible was heated while stirring the melt, and themelt was tapped in a rod shape at approximately 6 g/sec. The tap liquidwas rolled and cooled with a water cooling twin roller to prepare anamorphous body.

280 g of the obtained amorphous body was put into an electronic furnace,heated to 645° C. (crystallization temperature), and held at the sametemperature for 5 hours, and hexagonal strontium ferrite particles wereprecipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1,000 g of zirconia beads having a particle diameter of 1 mm,and 800 ml of an acetic acid aqueous solution having a concentration of1% were added to a glass bottle, and a dispersion process was performedin a paint shaker for 3 hours. After that, the obtained dispersionliquid and the beads were separated and put in a stainless still beaker.The dispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 19 nm, an activation volume was1,102 nm³, an anisotropy constant Ku was 2.0×10⁵ J/m³, and a massmagnetization σs was 50 A·m²/kg.

In Table 1, “ε-iron oxide” is an ε-iron oxide powder produced by thefollowing method.

4.0 g of ammonia aqueous solution having a concentration of 25% wasadded to a material obtained by dissolving 8.3 g of iron (III) nitratenonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg ofcobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and1.5 g of polyvinyl pyrrolidone (PVP) in 90 g of pure water, whilestirring by using a magnetic stirrer, in an atmosphere under theconditions of an atmosphere temperature of 25° C., and the mixture wasstirred for 2 hours still under the temperature condition of theatmosphere temperature of 25° C. A citric acid solution obtained bydissolving 1 g of citric acid in 9 g of pure water was added to theobtained solution and stirred for 1 hour. The powder precipitated afterthe stirring was collected by centrifugal separation, washed with purewater, and dried in a heating furnace at a furnace inner temperature of80° C.

800 g of pure water was added to the dried powder and the powder wasdispersed in water again, to obtain a dispersion liquid. The obtaineddispersion liquid was heated to a liquid temperature of 50° C., and 40 gof ammonia aqueous solution having a concentration of 25% was addeddropwise while stirring. The stirring was performed for 1 hour whileholding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS)was added dropwise and stirred for 24 hours. 50 g of ammonium sulfatewas added to the obtained reaction solution, the precipitated powder wascollected by centrifugal separation, washed with pure water, and driedin a heating furnace at a furnace inner temperature of 80° C. for 24hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1,000° C. wasfilled with the obtained precursor of ferromagnetic powder in theatmosphere and subjected to heat treatment for 4 hours.

The heat-treated precursor of ferromagnetic powder was put into sodiumhydroxide (NaOH) aqueous solution having a concentration of 4 mol/L, theliquid temperature was held at 70° C., stirring was performed for 24hours, and accordingly, a silicon acid compound which was an impuritywas removed from the heat-treated precursor of ferromagnetic powder.

After that, by the centrifugal separation process, ferromagnetic powderobtained by removing the silicon acid compound was collected and washedwith pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed byInductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), andGa, Co, and Ti substitution type ε-iron oxide(ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition,the X-ray diffraction analysis was performed under the same conditionsas the conditions described regarding the hexagonal strontium ferritepowder SrFe1 in advance, and it was confirmed that the obtainedferromagnetic powder has a crystal structure of a single phase which isan c phase not including a crystal structure of an α phase and a γ phase(ε-iron oxide type crystal structure) from the peak of the X-raydiffraction pattern.

Regarding the obtained (ε-iron oxide powder, an average particle sizewas 12 nm, an activation volume was 746 nm³, an anisotropy constant Kuwas 1.2×10⁵ J/m³, and a mass magnetization as was 16 A·m²/kg.

The activation volume and the anisotropy constant Ku of the hexagonalstrontium ferrite powder and the ε-iron oxide powder are values obtainedby the method described above regarding each ferromagnetic powder byusing an oscillation sample type magnetic-flux meter (manufactured byToei Industry Co., Ltd.).

In addition, the mass magnetization as is a value measured at themagnetic field strength of 1,194 kA/m (15 kOe) by using an oscillationsample type magnetic-flux meter (manufactured by Toei Industry Co.,Ltd.).

Example 1

Production of Magnetic Tape Cartridge

(1) Preparation of Alumina Dispersion

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a polyester polyurethaneresin including a SO₃Na group as a polar group (UR-4800 manufactured byToyobo Co., Ltd. (polar group amount: 80 meq/kg)), and 570.0 parts of amixed solvent solution of methyl ethyl ketone and cyclohexanone (massratio of 1:1) as a solvent were mixed with 100.0 parts of alumina powder(HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) having agelatinization ratio of 65% and a Brunauer-Emmett-Teller (BET) specificsurface area of 20 m²/g, and dispersed in the presence of zirconia beadsby a paint shaker for 5 hours. After the dispersion, the dispersionliquid and the beads were separated by a mesh and an alumina dispersionwas obtained.

(2) Magnetic Layer Forming Composition List

Magnetic Liquid

Ferromagnetic powder: 100.0 parts

Hexagonal barium ferrite powder having average particle size (averageplate diameter) of 21 nm (in Table 1, “BaFe”)

Magnetic layer dispersing agent: see Table 1

SO₃Na group-containing polyurethane resin: 14.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive Solution

Alumina dispersion prepared in the section (1): 6.0 parts

Silica Sol (Projection Formation Agent Liquid)

Colloidal silica (average particle size: 120 nm): 2.0 parts

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Stearic acid amide 0.2 parts

Butyl stearate: 2.0 parts

Polyisocyanate (CORONATE (registered product) L manufactured by TosohCorporation): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

The dispersing agent is a compound (a compound having apolyalkyleneimine chain and a vinyl polymer chain) described as acomponent of the magnetic layer forming composition of Example 1 inJP2019-169225A. As a component of the magnetic layer formingcomposition, a reaction solution obtained after the synthesis of theabove compound was used. The content of the dispersing agent in themagnetic layer shown in Table 1 which will be described later is anamount of the compound described above in such a reaction solution.

(3) Non-Magnetic Layer Forming Composition List

Non-magnetic inorganic powder: α-iron oxide: 100.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

carbon black: 20.0 parts

average particle size: 20 nm

SO₃Na group-containing polyurethane resin: 18.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Stearic acid: 2.0 parts

Stearic acid amide: 0.2 parts

Butyl stearate: 2.0 parts

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

(4) Back Coating Layer Forming Composition List

Carbon black: 100.0 parts

DBP (Dibutyl phthalate) oil absorption: 74 cm³/100 g

Nitrocellulose: 27.0 parts

Polyester polyurethane resin including sulfonic acid group and/or saltthereof: 62.0 parts

Polyester resin: 4.0 parts

Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., numberaverage molecular weight: 600): See Table 1

Stearic acid: see Table 1

Alumina powder (BET specific surface area: 17 m²/g): 0.6 parts

Methyl ethyl ketone: 600.0 parts

Toluene: 600.0 parts

Polyisocyanate (CORONATE L manufactured by Tosoh Corporation): 15.0parts

(5) Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod. A magnetic liquid was prepared by dispersing (beads-dispersing)components of the magnetic liquid with a batch type vertical sand millfor 24 hours. As dispersion beads, zirconia beads having a bead diameterof 0.5 mm were used. The prepared magnetic liquid, the abrasivesolution, and other components (silica sol, other components, andfinishing additive solvent) were mixed with each other andbeads-dispersed for 5 minutes by using the sand mill, and the treatment(ultrasonic dispersion) was performed with a batch type ultrasonicdevice (20 kHz, 300 W) for 0.5 minutes. After that, the obtained mixedsolution was filtered by using a filter having a hole diameter of 0.5μm, and the magnetic layer forming composition was prepared.

The non-magnetic layer forming composition was prepared by the followingmethod. The components described above excluding the lubricant (stearicacid, stearic acid amide, and butyl stearate) were kneaded and dilutedby an open kneader, and subjected to a dispersion process with atransverse beads mill disperser. After that, the lubricant (stearicacid, stearic acid amide, and butyl stearate) was added, and stirred andmixed with a dissolver stirrer, and a non-magnetic layer formingcomposition was prepared.

The back coating layer forming composition was prepared by the followingmethod. The components excluding polyisocyanate were introduced in adissolver stirrer and stirred at a circumferential speed of 10 msec for30 minutes, and the dispersion process was performed with a transversebeads mill disperser. After that, polyisocyanate was added, and stirredand mixed with a dissolver stirrer, and a back coating layer formingcomposition was prepared.

(6) Manufacturing Method of Magnetic Tape and Magnetic Tape Cartridge

The non-magnetic layer forming composition prepared in the section (5)was applied to a surface of a biaxial stretched support having the kindand thickness shown in Table 1 so that the thickness after the dryingbecomes a thickness shown in Table 1 and was dried to form anon-magnetic layer. Then, the magnetic layer forming compositionprepared in the section (5) was applied onto the non-magnetic layer sothat the thickness after the drying becomes a thickness shown in Table1, and a coating layer was formed. After that, a homeotropic alignmentprocess was performed by applying a magnetic field having a magneticfield strength of 0.3 T in a vertical direction with respect to asurface of a coating layer, while the coating layer of the magneticlayer forming composition is wet. Then, the drying was performed to formthe magnetic layer. After that, the back coating layer formingcomposition prepared in the section (5) was applied to the surface ofthe support on a side opposite to the surface where the non-magneticlayer and the magnetic layer were formed, so that the thickness afterthe drying becomes a thickness shown in Table 1, and was dried to form aback coating layer.

After that, a surface smoothing treatment (calender process) wasperformed by using a calender roll configured of only a metal roll, at aspeed of 100 m/min, linear pressure of 300 kg/cm), and a calendertemperature (surface temperature of a calender roll) of 90° C.

Then, the heat treatment was performed by storing the long magnetic taperaw material in a heat treatment furnace at the atmosphere temperatureof 70° C. (heat treatment time: 36 hours). After the heat treatment, themagnetic tape was obtained by slitting to have a width of ½ inches. Byrecording a servo signal on a magnetic layer of the obtained magnetictape with a commercially available servo writer, the magnetic tapeincluding a data band, a servo band, and a guide band in the dispositionaccording to a linear-tape-open (LTO) Ultrium format, and including aservo pattern (timing-based servo pattern) having the disposition andshape according to the LTO Ultrium format on the servo band wasobtained.

The servo pattern formed by doing so is a servo pattern disclosed inJapanese Industrial Standards (JIS) X6175:2006 and Standard ECMA-319(June 2001).

The magnetic tape (length of 960 m) after the servo signal recording waswound around the core for heat treatment, and the heat treatment wasperformed in a state of being wound around this core. As the core forheat treatment, a solid core member (outer diameter: 50 mm) formed of aresin and having 0.8 GPa of a modulus of bending elasticity was used,and the tension in a case of the winding was set as 0.6 N. The heattreatment was performed at the heat treatment temperature of 55° C. for5 hours. The weight absolute humidity in the atmosphere in which theheat treatment was performed was 10 g/kg Dry air.

After the heat treatment, the magnetic tape and the core for heattreatment were sufficiently cooled, the magnetic tape was detached fromthe core for heat treatment and wound around the core for temporarywinding, and then, the magnetic tape having the final product length(950 m) was wound around the reel (reel outer diameter: 44 mm) of themagnetic tape cartridge (LTO Ultrium 7 data cartridge) from the core fortemporary winding. The remaining length of 10 m was cut out and theleader tape based on section 9 of Standard European ComputerManufacturers Association (ECMA)-319 (June 2001) Section 3 was bonded tothe end of the cut side by using a commercially available splicing tape.

As the core for temporary winding, a solid core member having the sameouter diameter and formed of the same material as the core for heattreatment was used, and the tension in a case of winding was set as 0.6N.

As described above, a single reel type magnetic tape cartridge ofExample 1 in which a magnetic tape having a length of 950 m was woundaround a reel was manufactured.

The above steps were repeated to prepare three magnetic tape cartridges.Among the three magnetic tape cartridges, one magnetic tape cartridgewas used for the following (7) to (9), another magnetic tape cartridgewas used for the following (10), and still another magnetic tapecartridge was used for the following (11).

It can be confirmed by the following method that the back coating layerof the magnetic tape contains a compound formed of polyethyleneimine andstearic acid and having an ammonium salt structure of an alkyl esteranion represented by Formula 1.

A sample is cut out from a magnetic tape, and X-ray photoelectronspectroscopy analysis is performed on the surface of the back coatinglayer (measurement area: 300 μm×700 μm) using an ESCA device.Specifically, wide scan measurement is performed by the ESCA deviceunder the following measurement conditions. In the measurement results,peaks are confirmed at a position of a binding energy of the ester anionand a position of a binding energy of the ammonium cation.

Device: AXIS-ULTRA manufactured by Shimadzu Corporation

Excited X-ray source: Monochromatic Al—Kα ray

Scan range: 0 to 1,200 eV

Path energy: 160 eV

Energy resolution: 1 eV/step

Capturing Time: 100 ms/step

Number of times of integration: 5

In addition, a sample piece having a length of 3 cm is cut out from themagnetic tape, and Attenuated total reflection-fouriertransform-infrared spectrum (ATR-FT-IR) measurement (reflection method)is performed on the surface of the back coating layer, and, in themeasurement result, the absorption is confirmed on a wave numbercorresponding to absorption of COO⁻ (1,540 cm⁻¹ or 1,430 cm⁻¹) and awave number corresponding to the absorption of the ammonium cation(2,400 cm⁻¹).

(7) Recording of Data and Reproducing of Recorded Data on Magnetic Tapeafter Storage

The recording and reproducing before storage were performed using themagnetic tape device having the configuration shown in FIG. 1 . Therecording and reproducing head mounted on the recording and reproducinghead unit has 32 or more channels of reproducing elements (reproducingelement width: 0.8 μm) and recording elements, and servo signal readingand reproducing elements on both sides thereof.

The magnetic tape cartridge was placed in an environment having anatmosphere temperature of 23° C. and a relative humidity of 50% for 5days in order to make it familiar with the environment for recording andreproducing. Then, in the same environment, the recording and thereproducing were performed as follows.

The magnetic tape cartridge was set in the magnetic tape device and themagnetic tape was loaded. Next, while performing servo tracking, therecording and reproducing head unit records pseudo random data having aspecific data pattern on the magnetic tape. The tension applied in thetape longitudinal direction at that time is a constant value of 0.50 N.At the same time with the recording of the data, the value of the servoband interval of the entire tape length was measured every 1 m of thelongitudinal position and recorded in the cartridge memory.

Next, while performing servo tracking, the recording and reproducinghead unit reproduces the data recorded on the magnetic tape. At thattime, the value of the servo band interval was measured at the same timeas the reproducing, and the tension applied in the tape longitudinaldirection was changed so that an absolute value of a difference from theservo band interval during the recording at the same longitudinalposition approaches 0 based on the information recorded in the cartridgememory. During the reproducing, the measurement of the servo bandinterval and the tension control based on it are continuously performedin real time. In a case of such reproducing, the tension applied in thelongitudinal direction of the magnetic tape was changed in a range of0.50 N to 0.85 N by the control device of the magnetic tape device.Therefore, the maximum value of the tension applied in the longitudinaldirection of the magnetic tape during the reproducing is 0.85 N.

At the end of the reproducing, the entire length of the magnetic tapewas wound around the cartridge reel of the magnetic tape cartridge.

(8) Rewinding to Cartridge Reel (Rewinding before Storage) and Storage

Subsequently, in the above environment, the magnetic tape ran in themagnetic tape device and the entire length of the magnetic tape waswound on the winding reel of the magnetic tape device. The tensionapplied in the longitudinal direction of the magnetic tape during thewinding was set to a constant value of 0.50 N.

Then, tension was applied in the longitudinal direction of the magnetictape at a constant value of 0.40 N, and the entire length of themagnetic tape was wound on the cartridge reel (also referred to as“rewinding before storage”).

After the rewinding before storage, the magnetic tape cartridgeaccommodating the magnetic tape was stored for 48 hours in anenvironment with an atmosphere temperature of 60° C. and a relativehumidity of 20%. The inventors have surmised that this storage cancorrespond to long-term storage for about 10 to 20 years at anatmosphere temperature of 32° C. and a relative humidity of 55%.

(9) Evaluation of Recording and Reproducing Quality after Storage

After the storage, the magnetic tape cartridge was placed in anenvironment with an atmosphere temperature of 23° C. and a relativehumidity of 50% for 5 days in order to make it familiar with theenvironment for reproducing. Then, in the same environment, thereproducing was performed in the same manner as the reproducing beforestorage in the section (7). That is, the reproducing was performed bychanging the tension applied in the longitudinal direction of themagnetic tape as described above.

The number of channels in the reproducing described above was 32channels. In a case where all the data of 32 channels were correctlyread during the reproducing after the storage, the recording andreproducing quality was evaluated as “3”, in a case where data of 31 to28 channels were correctly read, the recording and reproducing qualitywas evaluated as “2”, and in other cases, the recording and reproducingquality was evaluated as “1”.

(10) Minimum Winding Deviation Occurrence Load

The minimum winding deviation occurrence load of the magnetic tape wasobtained by the method described above. An ultrasonic cutter was used toremove the upper and lower flanges. The load was applied by pressing theplate with a pressing device so that a uniform load was applied to theentire surface of the plate.

(11) Tape Thickness 10 tape samples (length: 5 cm) were cut out from anypart of the magnetic tape taken out from the magnetic tape cartridge,and these tape samples were stacked to measure the thickness. Thethickness was measured using a digital thickness gauge of a Millimar1240 compact amplifier manufactured by MARH and a Millimar 1301induction probe.

The value (thickness per tape sample) obtained by calculating 1/10 ofthe measured thickness was defined as the tape thickness.

Examples 2 to 24 and Comparative Examples 1 to 18

A magnetic tape cartridge was manufactured and various evaluations wereperformed in the same manner as in Example 1, except that the items inTable 1 were changed as shown in Table 1.

In the examples and comparative examples in which “Yes” is described inthe column of “Tension change during running” in Table 1, the tensionapplied in the longitudinal direction of the magnetic tape was changedwithin a range of the minimum value to maximum value in the same manneras in Example 1, and the reproducing before the storage was performed.

In the examples in which “None” is described in the column of “Tensionchange during running” in Table 1, the reproducing before the storagewas performed by applying the tension in the longitudinal direction ofthe magnetic tape at a constant value of 0.50 N.

In the examples and comparative examples in which the value of thetension is described in the column of “Rewinding tension before storage”in Table 1, the tension applied in the longitudinal direction of themagnetic tape during the rewinding (rewinding before storage) from thecartridge reel in the section (8) was set to the value shown in Table 1.

In the comparative examples in which “No rewinding” is described in thecolumn of the “Rewinding tension before storage” in Table 1, themagnetic tape cartridge accommodating the magnetic tape was stored for48 hours in the environment with the atmosphere temperature of 60° C.and a relative humidity of 20%, without performing the rewinding afterthe reproducing in the section (7).

In each of the examples and the comparative examples, the reproducingafter the storage was performed in the same manner as the reproducingbefore the storage. That is, during reproducing after the storage, thetension applied in the longitudinal direction of the magnetic tape andthe change in tension were the same as those during the reproducingbefore the storage.

The result described above is shown in Table 1 (Tables 1-1 to 1-4).

TABLE 1-1 Example Example Example Example Example Example Example 1 2 34 5 6 7 Kind of ferromagnetic powder BaFe BaFe BaFe BaFe BaFe BaFe BaFeThickness of magnetic layer 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm0.1 μm Thickness of non-magnetic layer 1.0 μm 1.0 μm 1.0 μm 1.0 μm 1.0μm 1.0 μm 1.0 μm Thickness of non-magnetic support 4.0 μm 4.0 μm 4.0 μm4.0 μm 4.0 μm 4.0 μm 4.0 μm Thickness of back coating layer 0.5 μm 0.5μm 0.5 μm 0.5 μm 0.5 μm 0.5 μm 0.2 μm Thickness of tape 5.6 μm 5.6 μm5.6 μm 5.6 μm 5.6 μm 5.6 μm 5.3 μm Kind of non-magnetic support PET PETPET PET PET PET PET Dispersing agent in magnetic layer 15.0 parts 15.0parts 2.0 parts 25.0 parts 15.0 parts 15.0 parts 25.0 partsPolyethyleneimine in back coating layer 2.0 parts 5.0 parts 3.0 parts5.0 parts 2.0 parts 2.0 parts 5.0 parts Stearic acid in back coatinglayer 0.2 parts 0.2 parts 0.2 parts 0.2 parts 0.2 parts 0.2 parts 0.2parts Minimum winding deviation 300N 250N 150N 50N 300N 300N 30Noccurrence load Tension change during running Yes Yes Yes Yes Yes YesYes Rewinding tension before storage 0.40N  0.40N  0.40N  0.40N   0.30N 0.20N  0.40N   Recording and reproducing 3 3 3 3 3 3 3 quality afterstorage Example Example Example Example Example 8 9 10 11 12 Kind offerromagnetic powder BaFe SrFe1 SrFe2 ε-iron BaFe oxide Thickness ofmagnetic layer 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm Thickness ofnon-magnetic layer 0.9 μm 1.0 μm 1.0 μm 1.0 μm 1.0 μm Thickness ofnon-magnetic support 3.8 μm 4.0 μm 4.0 μm 4.0 μm 4.0 μm Thickness ofback coating layer 0.2 μm 0.5 μm 0.5 μm 0.5 μm 0.5 μm Thickness of tape5.0 μm 5.6 μm 5.6 μm 5.6 μm 5.6 μm Kind of non-magnetic support PET PETPET PET PET Dispersing agent in magnetic layer 25.0 parts 15.0 parts15.0 parts 15.0 parts 15.0 parts Polyethyleneimine in back coating layer5.0 parts 2.0 parts 2.0 parts 2.0 parts 2.0 parts Stearic acid in backcoating layer 0.2 parts 0.2 parts 0.2 parts 0.2 parts 0.2 parts Minimumwinding deviation 20N 300N 300N 300N 300N occurrence load Tension changeduring running Yes Yes Yes Yes None Rewinding tension before storage0.40N   0.40N  0.40N  0.40N  0.40N  Recording and reproducing 3 3 3 3 2quality after storage

TABLE 1-2 Example Example Example Example Example Example 13 14 15 16 1718 Kind of ferromagnetic powder BaFe BaFe BaFe BaFe BaFe BaFe Thicknessof magnetic layer 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm Thickness ofnon-magnetic layer 1.0 μm 1.0 μm 1.0 μm 1.0 μm 1.0 μm 1.0 μm Thicknessof non-magnetic support 4.0 μm 4.0 μm 4.0 μm 4.0 μm 4.0 μm 4.0 μmThickness of back coating layer 0.5 μm 0.5 μm 0.5 μm 0.5 μm 0.5 μm 0.5μm Thickness of tape 5.6 μm 5.6 μm 5.6 μm 5.6 μm 5.6 μm 5.6 μm Kind ofnon-magnetic support PEN PEN PEN PEN PEN PEN Dispersing agent inmagnetic layer 15.0 parts 15.0 parts 20.0 parts 25.0 parts 15.0 parts15.0 parts Polyethyleneimine in back coating layer 2.0 parts 5.0 parts3.0 parts 5.0 parts 2.0 parts 2.0 parts Stearic acid in back coatinglayer 0.2 parts 0.2 parts 0.2 parts 0.2 parts 0.2 parts 0.2 partsMinimum winding deviation 300N 200N 100N 50N 300N 300N occurrence loadTension change during running Yes Yes Yes Yes Yes Yes Rewinding tensionbefore storage 0.40N  0.40N  0.40N  0.40N   0.30N  0.20N  Recording andreproducing 3 3 3 3 3 3 quality after storage Example Example ExampleExample Example Example 19 20 21 22 23 24 Kind of ferromagnetic powderBaFe BaFe SrFe1 SrFe2 ε-iron BaFe oxide Thickness of magnetic layer 0.1μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm Thickness of non-magnetic layer1.0 μm 0.9 μm 1.0 μm 1.0 μm 1.0 μm 1.0 μm Thickness of non-magneticsupport 4.0 μm 3.8 μm 4.0 μm 4.0 μm 4.0 μm 4.0 μm Thickness of backcoating layer 0.2 μm 0.2 μm 0.5 μm 0.5 μm 0.5 μm 0.5 μm Thickness oftape 5.3 μm 5.0 μm 5.6 μm 5.6 μm 5.6 μm 5.6 μm Kind of non-magneticsupport PEN PEN PEN PEN PEN PEN Dispersing agent in magnetic layer 25.0parts 25.0 parts 15.0 parts 15.0 parts 15.0 parts 15.0 partsPolyethyleneimine in back coating layer 5.0 parts 5.0 parts 2.0 parts2.0 parts 2.0 parts 2.0 parts Stearic acid in back coating layer 0.2parts 0.2 parts 0.2 parts 0.2 parts 0.2 parts 0.2 parts Minimum windingdeviation 25N 15N 300N 300N 300N 300N occurrence load Tension changeduring running Yes Yes Yes Yes Yes None Rewinding tension before storage0.40N   0.40N   0.40N  0.40N  0.40N  0.40N  Recording and reproducing 33 3 3 3 2 quality after storage

TABLE 1-3 Comparative Comparative Comparative Comparative ComparativeExample 1 Example 2 Example 3 Example 4 Example 5 Kind of ferromagneticpowder BaFe BaFe BaFe BaFe BaFe Thickness of magnetic layer 0.1 μm 0.1μm 0.1 μm 0.1 μm 0.1 μm Thickness of non-magnetic layer 1.0 μm 1.0 μm1.0 μm 1.0 μm 1.0 μm Thickness of non-magnetic support 4.0 μm 4.0 μm 4.0μm 4.0 μm 4.0 μm Thickness of back coating layer 0.5 μm 0.5 μm 0.5 μm0.5 μm 0.5 μm Thickness of tape 5.6 μm 5.6 μm 5.6 μm 5.6 μm 5.6 μm Kindof non-magnetic support PET PET PET PET PET Dispersing agent in magneticlayer None None None None None Polyethyleneimine in back coating layerNone None None None None Stearic acid in back coating layer None NoneNone None None Minimum winding deviation 400N 400N 400N 400N 400Noccurrence load Tension change during running Yes Yes Yes Yes YesRewinding tension before storage No 0.50N  0.40N  0.30N  0.20N rewinding Recording and reproducing 1 1 1 1 1 quality after storageComparative Comparative Comparative Comparative Comparative Example 6Example 7 Example 8 Example 9 Example 10 Kind of ferromagnetic powderBaFe BaFe BaFe BaFe BaFe Thickness of magnetic layer 0.1 μm 0.1 μm 0.1μm 0.1 μm 0.1 μm Thickness of non-magnetic layer 1.0 μm 1.0 μm 1.0 μm1.0 μm 1.0 μm Thickness of non-magnetic support 4.5 μm 4.5 μm 4.0 μm 4.0μm 4.0 μm Thickness of back coating layer 0.5 μm 0.5 μm 0.5 μm 0.5 μm0.5 μm Thickness of tape 6.1 μm 6.1 μm 5.6 μm 5.6 μm 5.6 μm Kind ofnon-magnetic support PET PET PET PET PET Dispersing agent in magneticlayer None None None 10.0 parts 15.0 parts Polyethyleneimine in backcoating layer None None 5.0 parts 0.2 parts 1 part Stearic acid in backcoating layer None None 0.2 parts 0.2 parts 0.2 parts Minimum windingdeviation 500N 500N 380N 350N 320N occurrence load Tension change duringrunning Yes Yes Yes Yes Yes Rewinding tension before storage No 0.20N 0.40N  0.40N  0.40N  rewinding Recording and reproducing 1 1 1 1 1quality after storage

TABLE 1-4 Comparative Comparative Comparative Comparative ComparativeComparative Comparative Comparative Example 11 Example 12 Example 13Example 14 Example 15 Example 16 Example 17 Example 18 Kind offerromagnetic BaFe BaFe BaFe BaFe BaFe BaFe BaFe BaFe powder Thicknessof magnetic 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1 μmlayer Thickness of 1.0 μm 0.9 μm 1.0 μm 1.0 μm 1.0 μm 1.0 μm 1.0 μm 0.9μm non-magnetic layer Thickness of 4.0 μm 3.8 μm 4.0 μm 4.0 μm 4.0 μm4.0 μm 4.0 μm 3.8 μm non-magnetic support Thickness of back 0.2 μm 0.2μm 0.5 μm 0.5 μm 0.5 μm 0.5 μm 0.2 μm 0.2 μm coating layer Thickness oftape 5.3 μm 5.0 μm 5.6 μm 5.6 μm 5.6 μm 5.6 μm 5.3 μm 5.0 μm Kind ofnon-magnetic PET PET PEN PEN PEN PEN PEN PEN support Dispersing agent inNone None None None 10.0 parts 15.0 parts None None magnetic layerPolyethyleneimine in None None None 5.0 parts 0.2 parts 1.0 part NoneNone back coating layer Stearic acid in back None None None 0.2 parts0.2 parts 0.2 parts None None coating layer Minimum winding 380N 350N480N 450N 400N 350N 450N 400N deviation occurrence load Tension changeduring Yes Yes Yes Yes Yes Yes Yes Yes running Rewinding tension before0.40N  0.40N  0.40N  0.40N  0.40N  0.40N  0.40N  0.40N  storageRecording and reproducing 1 1 1 1 1 1 1 1 quality after storage

From the results shown in Table 1, it can be confirmed that excellentrecording and reproducing quality could be obtained after storage in theexamples.

One embodiment of the invention is advantageous in a technical field ofvarious data storages such as archives.

What is claimed is:
 1. A magnetic tape cartridge comprising: a magnetictape; and a cartridge reel, wherein, in the magnetic tape, a minimumwinding deviation occurrence load measured after the magnetic tape isrewound around the cartridge reel by applying a tension of 0.40 N in alongitudinal direction of the magnetic tape is 300 N or less, theminimum winding deviation occurrence load being obtained by thefollowing method at 23° C. and 50% relative humidity: providing anunused magnetic tape cartridge; temporarily extracting the entire lengthof the magnetic tape from the cartridge by applying a tension of 0.40 Nin the longitudinal direction of the magnetic tape and winding themagnetic tape around a temporary winding reel; rewinding the entirelength of the magnetic tape from the temporary winding reel around thecartridge reel by applying a tension of 0.40 N in the longitudinaldirection of the magnetic tape; extracting the cartridge reel aroundwhich the entire length of the magnetic tape is wound from thecartridge, said cartridge reel including at least a reel hub andoptionally flanges protruding outward in a radial direction from anupper end portion and a lower end portion of the reel hub, respectively;for a cartridge reel having flanges, removing the flanges to expose bothsides of a tape winding surface around which the magnetic tape is wound;installing the reel hub on a cradle; placing an aluminum ring having anouter diameter of 90 mm and an inner diameter of 80 mm on the tapewinding surface of the wound magnetic tape installed on the cradle sothat the center of rotation of the reel hub and the center of thealuminum ring match to each other within a deviation of 3 mm or less;placing an aluminum plate having a square shape of 100 mm×100 mm and athickness of 3 mm in a plan view on the aluminum ring; and applying aload from the top of the plate, holding it for 10 minutes, and thenremoving it, in the following manner: in a case where the position in avertical direction of the upper surface of the plate before applying theload is defined as A, the position in the vertical direction of theupper surface of the plate after removing the load is defined as B, and“A−B≥1 mm” is satisfied, it is considered that an unwinding has occurredon the wound magnetic tape; starting the load application from 5 N withrespect to the magnetic tape being measured, performing measurementswhile increasing the load in increments of 5 N, and defining the minimumload at which said unwinding is considered to have occurred as theminimum winding deviation occurrence load.
 2. The magnetic tapecartridge according to claim 1, wherein the magnetic tape includes anon-magnetic support, and a magnetic layer including a ferromagneticpowder, and the non-magnetic support is a polyester support.
 3. Themagnetic tape cartridge according to claim 2, wherein the magnetic tapefurther includes a non-magnetic layer including a non-magnetic powderbetween the non-magnetic support and the magnetic layer.
 4. The magnetictape cartridge according to claim 2, wherein the magnetic tape furtherincludes a back coating layer containing a non-magnetic powder on asurface side of the non-magnetic support opposite to a surface sideprovided with the magnetic layer.
 5. The magnetic tape cartridgeaccording to claim 1, wherein the magnetic tape has a tape thickness of5.6 μm or less.
 6. The magnetic tape cartridge according to claim 1,wherein the magnetic tape has a tape thickness of 5.3 μm or less.
 7. Themagnetic tape cartridge according to claim 1, wherein the minimumwinding deviation occurrence load is 10 N to 300 N.
 8. The magnetic tapecartridge according to claim 1, wherein the magnetic tape cartridge isused in a magnetic tape device in which the magnetic tape is caused torun between a winding reel and the cartridge reel of the magnetic tapecartridge in a state where a tension is applied in the longitudinaldirection of the magnetic tape, a maximum value of the tension being0.50 N or more, and the magnetic tape after running in a state where thetension is applied is caused to be wound around the cartridge reel byapplying a tension of 0.40 N or less in the longitudinal direction ofthe magnetic tape.
 9. A magnetic tape device comprising: the magnetictape cartridge according to claim
 1. 10. The magnetic tape deviceaccording to claim 9, comprising: the magnetic tape cartridge; and awinding reel, wherein the magnetic tape is caused to run between thewinding reel and the cartridge reel of the magnetic tape cartridge in astate where a tension is applied in the longitudinal direction of themagnetic tape, a maximum value of the tension being 0.50 N or more, andthe magnetic tape after running in a state where the tension is appliedis caused to be wound around the cartridge reel of the magnetic tapecartridge by applying a tension of 0.40 N or less in the longitudinaldirection of the magnetic tape.
 11. The magnetic tape device accordingto claim 10, wherein the tension applied in the longitudinal directionof the magnetic tape during the running is changed.